3DS XL released a little more than a year after the original launch, so a revision <20 mos. is possible or fall 2018.
A big question is about the chipset of Switch. So many reports about "20nm not catching on as a standard node, 16nm was the real next step, it will cost Nvidia more to produce on the old fab/trying to clear inventory giving Nintendo a sweet deal on their X1 chip" etc etc etc...when will the shift to X2 (more power efficient and 50% faster) be officially made?
I expect Switch Lite/mini to be the first revision. "Lite" not only in regards to size but features as well. with a smaller model, there will be no joycons. The controls will return to a more comfortable layout as you see with the pro controller; the direct top/bottom button layout was necessary due to individual joycon play. This also means no dock, that will be sold separate and expect a 2.0 design similar to the one from Nyko . I expect this model to pretty much look like a Vita.
Same chipset should take advantage of the gains and get an XL or MAX model (same physical size but bigger screen via shrunken bezel) in 2019. Question is , will the screen be 1080p (max performance at all times) and will the battery life perform similar to the launch model? On top of that, the original Switch should get phased out as well unless they just stick the new chips in those old, fat bezel switches...The XL/MAX will be very popular, so Im not sure if they even keep the oddball 6.2 inch model around.
Nintendo has an extensive history with portable redesigns, and I expect more HW variants than ever now with NVidia as their partner.