I actually don't think the Tegra X2 will offer that much of an improvement over the X1. 20nm vs 16nm. 7nm is the hot chip size now and the jump from 20 to 7 would be a generational leap.
In terms of specs. It's would be very noticable. For the same power draw as X1's 20nm, we're getting
-1.5x the GPU(GFLOPS),
-2X the CPU(Denver cores would help a lot and make it equal to PS4 at least),
-2X the amount of RAM(4GB to 8GB),
-and a little over 2X the amount of bandwidth as well(25GB/s vs 58GB/s).
Or it could have twice the energy efficiency/power draw as the x1 with the same cpu and gpu clockspeeds. It would close the distance with Xbone specs.
I wouldn't be surprised if we get:
-Odyssey and Botw from 900p to 1080p with even more stable framerate
-Xenoverse 2 with 1080p docked, 720p handheld and 60fps for all modes. It would miss the anti-aliasing of PS4 version.
Mario Kart 8 Deluxe 60fps for 3-4 players
-60fps for RE Revelations and 60fps unlocked for RE Revelations 2
-720p native(or 900p adaptive) for docked mode and 720p adaptive for handheld for DOOM with 60fps, with some added effects closer to xbone/ps4
-900p docked and 720p handheld for xenoblade chronicles 2, with significantly more stable framerate. Resolution may be adaptive.
-900p docked/720p handheld native for rocket league with some better effectss
to name a few
Buut.. 16nm is relatively outdated for 2017 for a handheld(x-box one x is using 16nm, but that's for a home console), and current flagship mobile phones right now are using 10nm. I do agree that the Switch iteration should use something in the 7nm to 10nm, which is doable 2 years from now.
We could have something like Xavier where it would have 2x the power as X2(or 3x the current x1/switch). Handheld mode would at least be as powerful as current switch docked mode, and docked mode would be above Xbone in GPU and trading blows with PS4. If we have 1.5 TFLOPS(and not the locked at 80% thing due to over heating), the newer architecture should make it more powerful than PS4 in GPU/graphics. Current xavier is speculated to be at 16nm, but I'm sure they'll downsize it to 10nm or w/e.