It doesn't really matter what TF Switch 2 has when it is docked, it will be memory bandwidth starved anyway. Nintendo will likely use Lpddr5 which will bring about 50GB/s bandwidth on 64-bit bus or around 100GB/s bandwidth on 128-bit bus. If Nintendo planning to rely on DLSS 2 I would guess they will go for 64-bit bus.
I would think they would go with better than LPDDR5, if they want next-gen ports. Even on 128 bit bus, that would give them less than 1/3rd the speed of Xbox Series X's slower CPU/OS focused 336 GB/s RAM, less than 1/4th the speed of PS5's 448 GB/s RAM, and less than 1/5th the speed of Series X's faster GPU focused 560 GB/s RAM. Maybe they could go with some kind of hybrid LPPDR5/GDDR6 setup or hybrid LPDDR5/eSRAM setup or something.