[RMVX ACE] MULTIPLE ENGINES IN A GAME?

An interesting question. I dont believe so, simply because the nature of most scripts is to extend existing functionality, which essentially clobbers out everything else. There is theoretically a way to do so, but it would involved knowledge of each piece of the system your scripts are using, how they overlap, and then creating duplicates of the base modules to override instead of the originals.. and then creating some sort of script to swap between the originals and the copies.

Short answer: theres no easy way to do it. It would be pretty damn hard and complicated.