Just some thoughts:

#run can run anything, if you don't trust the codebase you have to check everything for malicious calls. ( #run format c: as a joke :-/ when you compile )

check functions seem to have limited use. They can't check for input that isn't hardcoded( or can they? ). A runtime check might be more valuable.

I don't remember if it was mentioned; I think having C like implicit conversions is a bad idea. If types don't match exactly, cast or give an error.

defer is interesting, do you get an error if you try to return an object which is also defered getting deleted?