said, DS and PS1 is certainly a possibility, and without much trouble if RA comes out soon enough.
PSP and Dreamcast is also possible, but I assume this one might struggle a bit with certain games.
PS2... Hard to say to be honest.
It could run for sure, but to what extent... That's what's left to be seen.
PS3 is of course an absolute NO
, it requires way too much horse power to get it running, which the Switch lacks by a great margin.