I'd honestly take a Mario & Luigi over a Paper Mario anyday. PM has such a watered-down and really simple fighting style that is boring to play with. I'd rather have the fast-paced and actual technical styles introduced in Mario & Luigi.
As for a possibility of another SMRPG or a simple remake, it's not totally out of the question. Square Enix now has a returned friendship and interest to Nintendo so I don't see why they can't partner up again. Plus, many of the members who work on Mario & Luigi are Square Enix staff (including Yoko Shimomura, the composer for SMRPG and the Mario & Luigi series).