How long ago would they have been working on this new dlc for Starlink though because I'm pretty sure some insiders heard about the Starfox GP by Retro since 2017.
So, as a possible scenario... (and as you know from our earlier exchanges, I really hope this is wrong).
2014 Retro working on Star Fox.
2016 Star Fox is terminated due to development hell.
2016 Nintendo internally green light Metroid Prime 4
2016 Retro working on Metroid Prime Trilogy HD.
2017 Metroid Prime 4 announced, developed by Namco Bandai
2017 Retro salvage part(s) of their Star Fox game and it gets fed into Starlink.
2018 Metroid Prime 4 is in development hell.
2018 Retro completes Metroid Prime Trilogy HD, and also creates a "Here's how we'd do MP4"
2018 Nintendo impressed by Metroid Prime Trilogy and the "Here's how we'd do MP4".
2019 Metroid Prime 4 is rebooted with Retro at the helm.
2019 Metroid Prime Trilogy HD launched, developed by Retro.
To be clear, development hell is an exaggeration. Sometimes a game just doesn't work. If Retro felt there were decent elements, but not a complete game, then I absolutely believe they would be proactive with it (like they clearly were proactive with MP4 too) and put forward a business case for its inclusion in Starlink.