If publishers adopt a wait and see approach, so will consumers, and the combination of both could be fatal.
I don't think all publishers are adopting a wait and see approach though. I think the reality of the market in Japan today shows that publishers of the biggest PSP games have already made their primary decisions.
Capcom:
MHP3 (PSP) -> MH4 (3DS)
Konami:
MGS PW (PSP) -> Next Kojima Game (PS3/360/Vita)
Square Enix:
KH BbS (PSP) -> KH3D (3DS)
The ones who are doing a wait and see approach seem to be Sega (Phantasy Star Portable, Project Diva) and Bandai Namco (God Eater, Tales of the World, Gundam). They're putting their smaller portable franchises on both platforms, or neither, or a different spinoff to test the market (Project Diva). They don't seem to have really decided where they will settle the successor of their PSP franchises yet, but the bigger players definitely have.