Agreed with
@SarahKerrigan and
@Jimzz here. Why not just a simple shrink of the current X1 instead? God knows the Switch can use a clock speed bump, so a conservative GPU clock speed of 500 MHz undocked, 1 GHz docked (to keep the 1:2 ratio) plus a bit on the CPU side are easily achievable. Boost clocks notwithstanding. TSMC's 16/12 FFC provides up to 60% lower power or 50% higher perf over its 20nm so Nvidia & Nintendo have plenty of room.
8GB of DRAM would be nice but I'm a bit skeptical on that. Undocked should maintain docked's 1600 MHz at least. 64GB of NAND should be a given, at least on the higher end model.
To speculate even further, the cheaper "Switch Go" will have integrated controllers, no bundled dock, updated SoC and target the $200 price bracket. The "New Switch" will replace the current one - with updated SoC, double the NAND, larger battery and display while keeping the form factor to maintain compatibility with current Joy-cons and dock. A late 2019 release bundle with Pokemon practically prints money.