Virtual Computer 4 feature requests

I'm starting work on Virtual Computer 4 and stopping software development on Virtual Computer 3. I will be publishing my personal software library for VC3 shortly. I want Virtual Computer 4 to handle things such as multitasking and subroutine calls better, while still being easy to program. I'm open to completely redesigning the architecture, but I most likely won't. I will be removing the flag lock, as even on VC3 it was a legacy feature never used. Other than that, I have no plans, so I'll take suggestions! Please post anything you'd like to see in VC4.