I'm curious if they can take advantage of vfork / CLONE_VM, to get the benefits of sharing memory and lower overhead context switches, with the trade of still getting benefits from the scheduler, and sysadmin-friendliness.

The other thing that might be interesting is FUTEX_SWAP / UMCG. Although it doesn't remove the overhead induced by context switches entirely (specifically, you would still deal with TLB misses), you can avoid dealing with things like speculative execution exploit mitigations.