Or putting it another way, take the PS2 with this new hardware shrink, put it in a Apple-esque white box, sell it as PlayStation Waggle and announce it also has complete BC with PS2 as well! For development, a lot of titles could be rushed out, such as Katamari. Just map it to motion instead of analogue sticks, and you've got a Wii-esque game. Similarly that stunt racing thing PS2/PSP had that's a PS3 download. If there's enough re-engineered PS2 titles mapped to motion, Sony would only need to provide a few key 1st party titles along the lines of Play and Sports to offer the same multiplayer motion experience as Wii at less money. As the replacement for PS2, you'll still sell a few hundred thousand a month without any greater uptake than PS2 has now. Offer a peripheral to add the functions to the existing PS2 userbase, and getting a few million users shouldn't be too hard, by which point it'll be a viable cross-platform machine for Wii titles.
If Sony had a mind to implement it, it seems to me they could.