With the timely announcement of new Indie games coming to Switch, I've tried to compile sales reports for notable Indie games released on Switch so far. If I have missed any reports (whether more recent updates or updates for games not currently included), please post the source and I'll update the OP.
As a summary, most of the reports so far are overwhelmingly positive, with Switch versions in many cases being the highest selling and in some cases even outselling all other versions combined. I could only find one report stating that the developers were not happy with sales so far. (Note: there is of course a bias in reporting success stories over failures, but the number of successes is something to note as well). There are also other games that are likely successful, but I couldn't fine reports from the developers (Rocket League, Golf Story, etc.)
Now, why are Indies seemingly doing so well on Switch?
My thoughts:
1) Well suited for platform: smaller games are great for portable play, Indie games have less performance and visual compromises on the less powerful Switch hardware.
2) Well suited for the audience: the Switch userbase is currently enthusiast and active. Many Indie games echo older aesthetics, genres, and playstyles that the older Nintendo gamers grew up with and that Nintendo still actively cultivates (2D platformers, metroidvanias, etc.)
3) Less competition: some people will claim that these games are only doing well because there are currently less games on the eShop with the Switch being a new system, but I don't think this is a big factor. Current gen systems were also new at one point, and it seems indies on Switch are outperforming even when launch aligned. However, the Switch as and will continue to miss many third party AAA games, thus leaving more room for Indie games to shine.
4) No virtual console: people having been asking for VC on Switch since before it launched, but the truth is that the popularity of Nintendo's classics would completely overwhelm Indie titles. I think if Nintendo wants to continue to let Indies thrive on Switch, they'll need to rethink how they distribute their classic content. Releasing classic games one by one all over again will overshadow new Indie games.
As a summary, most of the reports so far are overwhelmingly positive, with Switch versions in many cases being the highest selling and in some cases even outselling all other versions combined. I could only find one report stating that the developers were not happy with sales so far. (Note: there is of course a bias in reporting success stories over failures, but the number of successes is something to note as well). There are also other games that are likely successful, but I couldn't fine reports from the developers (Rocket League, Golf Story, etc.)
Now, why are Indies seemingly doing so well on Switch?
My thoughts:
1) Well suited for platform: smaller games are great for portable play, Indie games have less performance and visual compromises on the less powerful Switch hardware.
2) Well suited for the audience: the Switch userbase is currently enthusiast and active. Many Indie games echo older aesthetics, genres, and playstyles that the older Nintendo gamers grew up with and that Nintendo still actively cultivates (2D platformers, metroidvanias, etc.)
3) Less competition: some people will claim that these games are only doing well because there are currently less games on the eShop with the Switch being a new system, but I don't think this is a big factor. Current gen systems were also new at one point, and it seems indies on Switch are outperforming even when launch aligned. However, the Switch as and will continue to miss many third party AAA games, thus leaving more room for Indie games to shine.
4) No virtual console: people having been asking for VC on Switch since before it launched, but the truth is that the popularity of Nintendo's classics would completely overwhelm Indie titles. I think if Nintendo wants to continue to let Indies thrive on Switch, they'll need to rethink how they distribute their classic content. Releasing classic games one by one all over again will overshadow new Indie games.
Game Sales Source Date
Steamworld Dig 2 10x Steam"}">>10x Steam https://waypoint.vice.com/en_us/article/kzgq7y/steamworld-dig-2-sales-switch 12/1/17
Blossom Tales 20x Steam"}">>20x Steam https://nintendoeverything.com/blos...-now-surpassed-steam-sales-by-a-factor-of-20/ 8/27/18
Death Squared PC, PS4, Xbox One combined"}">>PC, PS4, Xbox One combined https://www.vg247.com/2017/09/15/se...ing-much-better-on-switch-than-anywhere-else/ 9/15/17
Oceanhorn PC, PS4, Xbox One combined"}">>PC, PS4, Xbox One combined https://www.vg247.com/2017/09/15/se...ing-much-better-on-switch-than-anywhere-else/ 9/15/17
Wonder Boy PC, PS4, Xbox One combined"}">>PC, PS4, Xbox One combined https://www.vg247.com/2017/09/15/se...ing-much-better-on-switch-than-anywhere-else/ 9/15/17
Wulverblade PC, PS4, Xbox One combined"}">>PC, PS4, Xbox One combined https://nintendoeverything.com/wulverblade-dev-puts-strong-switch-sales-into-perspective/ 5/28/18
Stardew Valley ~1M https://comicbook.com/gaming/2018/04/27/stardew-valley-nintendo-switch-overcooked-sales/ 4/27/18
Overcooked ~500k https://comicbook.com/gaming/2018/04/27/stardew-valley-nintendo-switch-overcooked-sales/ 4/27/18
Fast RMX 100k https://gonintendo.com/stories/289279-shin-en-on-fast-rmx-sales-requests-for-switch-ports-next-game 9/3/17
Blaster Master Zero 110k Switch + 3DS https://twinfinite.net/2017/10/master-blaster-zero-sales-milestone/ 8/3/17
Kamiko 200k https://nintendowire.com/news/2018/...-sales-switch-fairune-collection-coming-soon/ 4/9/18
Hollow Knight 250k in two weeks http://www.ign.com/articles/2018/06...50000-copies-on-switch-in-its-first-two-weeks 6/29/18
Snipperclips 350k http://www.nintendoworldreport.com/...g-news-snipperclips-sales-e3-and-mobile-plans 4/27/17
Shovel Knight 370k (highest revenue, fastest sales) http://yachtclubgames.com/2018/04/two-million-copies-of-shovel-knight-sold/ 4/11/2018
Brawlout 50k http://www.nintendolife.com/news/2018/01/brawlout_has_passed_50k_sales_on_the_switch 1/3/18
Graceful Explosion Machine 50k http://www.vertexpop.com/blog/graceful-explosion-machine-one-year-later/ 4/12/18
Voez 50k https:///kamiko-voez-continue-break-sales-milestones-switch/ 1/1/18
Sonic Mania Plus PC, PS4, Xbox One combined)"}">52% (>PC, PS4, Xbox One combined) https://comicbook.com/gaming/2018/07/25/nintendo-switch-sonic-mania-plus-biggest-seller-sega/ 7/25/18
Bloodstained: Curse of the Moon PC, PS4, Xbox One combined)"}">56% (>PC, PS4, Xbox One combined) https://nintendoeverything.com/over-50-of-bloodstained-curse-of-the-moons-sales-have-been-on-switch/ 6/5/18
Mutant Mudds Collection 7,500k (Just OK) https://www.dualshockers.com/mutant...ls-ok-nintendo-switch-despite-marketing-push/
Enter the Gungeon 75k in two weeks https://www.pcgamer.com/indie-veterans-on-the-state-of-indie-games-on-nintendo-switch-versus-steam/ 3/14/18
Mighty Gunvolt Burst 80k Switch + 3DS https://www.perfectly-nintendo.com/...demo-now-available-free-dlc-character-unlock/ 12/30/17
Furi Exceeded expectations, ~PC http://www.n-europe.com/news/furi-s...unch-on-switch-for-developers-the-game-bakers 2/6/18
Super Meat Boy first day sales close to debut on Xbox 360 https://www.pcgamer.com/indie-veterans-on-the-state-of-indie-games-on-nintendo-switch-versus-steam/ 3/14/18
West of Loathing Happy (1/3 of PC sales) https://www.destructoid.com/west-of...-but-the-team-is-still-thrilled--509470.phtml 6/25/18
Darkest Dungeon Happy with performance https://www.pcgamer.com/indie-veterans-on-the-state-of-indie-games-on-nintendo-switch-versus-steam/ 3/14/18
Snake Pass Happy with performance https://www.gonintendo.com/stories/...alk-switch-performance-sales-cut-ideas-amiibo 6/4/17
Axiom Verge PS4 launch sales"}">Launch Sales >PS4 launch sales https://www.dualshockers.com/axiom-verge-sales-nintendo-switch-ps4-indie/ 2/2/18
Celeste Most on Switch https://nintendoeverything.com/celeste-has-sold-the-most-on-switch/ 2/3/18
Has Been Heroes Most on Switch https://gonintendo.com/stories/291991-switch-version-of-has-been-heroes-sold-the-best-says-developer 10/3/17
Thimbleweed Park Most on Switch https://forums.thimbleweedpark.com/t/twp-players-on-steam-revealed/2891/15 7/5/18