I also imagine a future of three SKUs: Original, "Lite/Slim" coming soon, and eventually a "Switch 2" version later. Eventually the "Original" would go away and be replaced by the "Slim", and then we'd be moving forward with just a lower-powered "Lite" and a bigger, more expensive, more capable "Switch 2".
My thinking is that even though we talk about form factor with a "Lite", what's more important is price. The "Lite" is actually a play to start replacing the 3DS niche, so it needs to hit or get close to $200, and if it happens to be smaller then that's just a bonus. Nintendo already experimented with selling a Dockless Switch in Japan for around $250 so maybe that's not too far away. I guess a Switch "Lite" will not come with a dock (Nintendo could sell that separately) but I wonder where the other $50 cost savings could come from.
I am definitely warming up to a Tegra X2 as probably where Nintendo could go for a Switch "Lite" revision. From my understanding, the Tegra X2 is very similar to a Tegra X1 except at a newer 16nm manufacturing process. It doesn't seem to offer enough performance improvements to be a true generational leap, so it's more about using that for power efficiency than trying to force some sort of half-generational step. Apparently the Tegra X2's "Max-Q" underclocked setting seems able to match (or beat) the Switch's Docked mode at what sounds like the handheld mode's power draw. I really don't see this hardware getting any exclusive software, technically I think it could get 50% more GPU performance than the current Switch docket, but I can't imagine it'd be safe to change the CPU speed on unaware devs (handheld and docked Switch maintains the same CPU speed).
Since the cost might be the most important aspect of a Switch "Lite" then I don't see them springing for a better screen or any new or advanced features. In fact, I think they'll take the power savings from the X2 chipset, and use it not for longer battery life but for a smaller battery. Everything would be funneled not at creating a better experience, but a more accessible and inexpensive one. Hopefully they continue to pack in AC Adapters though...
If this thing could hit the $200 price point at launch or within a year, then I'd see space for Nintendo to design a real Switch "2" generational leap. That I'm not so sure what it'd look like. I assume it'd still be a Switch, possibly even slightly larger than the one we have right now. What I'm not so sure about is what the innards will be: Nvidia's Tegra after the X2 have all been drastically different, more designed for Automated Driving or AI. I imagine that Nintendo will ask Nvidia to design a Tegra X2 successor moving off of A57 cores and onto something like A73 CPU cores at least which I'm guessing could double CPU performance, or even newer A75 or A76 chips. The GPU might be more challenging, after the Tegra X2's Pascal the next Nvidia consumer architecture is Turing (skipping Volta), but those chipsets just came out these last few months. My rule of thumb is that Nintendo wants to use tech that's two years old in order to keep costs down, but that'd mean that Volta GPU tech wouldn't qualify until 2021 and that seems pushing it. However, if the Switch "Lite" can keep the platform affordable at $200, then enthusiasts could be the target for a $349 or even $400 "Switch 2" in 2020 that uses cutting edge tech yet can still play all the Switch 1 games, which could also have "Switch 2 Performance" modes to take advantage of the new tech.
Even with all this improvement, maybe the best we could expect from this 2020/2021 "Switch 2" I'm wondering if the GPU rating on this "Switch 2" could cross the 1 TFLOP level. Obviously the Switch is already getting some Xbox One and PS4 ports even though it's anywhere from 200-400 Nvidia-style GFLOPS versus the 1.1 AMD-style Gflops of the Xbox One, but the next gen Sony and Xbox consoles are rumored to stretch from 4-10 AMD-style TFlops in 2020.
Perhaps a "Switch 2 Lite" would be the next target model, and then finally a "Switch 3" which would start having exclusive games that could no longer run on "Gen 1" Switches (Original/Lites). I wonder if by this point there could be "Gen 1" or "Gen 2" Switches that hit the $150 price point or better.