If they want to keep the current Switch relevant, and they should, the new hardware can't be too far off in terms of power; though this time, they might go for a custom chip as well.
That being said, an X2 with little or no underclocking would be quite a step up from a the underclocked X1 powering the Switch right now.
Nintendo is both in a great and a tough spot. The Switch concept is amazing because it makes possible to play roughly similar games on the go than what we played only in our living rooms so far. They were smart to take advantage of the fact that mobile technology has evolved far enough to allow for a portable device to play Doom, Ark, or Warframe.
That being said, the new generation of console is just around the corner and while cross-gen titles will probably exist, the Switch is going to have a hard time keeping up in terms of power and could be downgraded from "hybrid console" to "another Nintendo handheld" in the global perception and in the scope of third party releases. This is why I believe that they are bound to release a more powerful device rather sooner than later (September 2020 would be my bet), while keeping the current switch alive for a few more years after (till 2022 at least). Hence the comparison with the smartphone market where phones from 4-5 years ago can still play most of the modern games with gimped performances. In that sense, Nintendo is back in the power race, except it's a race where the challenge for them will be to stay close enough from their competitors to receive some third party support for some multiplatform games to be developed with Nintendo's console in mind as well; it's something that was mentioned recently by Panic Button, where they basically said that Doom and Wolf 2 hadn't been developed with the Switch as a possible platform, but that future 3rd party game may take this new parameter into account rendering ports easier. I wouldn't be surprised if the next Doom of Wolfenstein look significantly better and run smoother on Switch than the ones we have now.
Overall the Switch is always going to be about compromises, and they've done a good job so far hardware-wise. I have nothing but my opinion to support this, but I sincerely believe that a new hardware will be released in 2020, and that either new Splatoon, Mario Kart, Zelda or Mario will be released to push its sales.
