Well, I don't know anything about the systems, but PSP is already obsolete and PS Vita is still in his Prime and has more potential
what you have in mind is very good at issue the portability
I googled and found this
PSP-Series - (1000 = 32 MB Ram), (2000 = 64 MB Ram) and (3000 = 64 MB Ram). with just this amount of Ram, won't tolerate the Unity engine