rather than a one-size-fits-all VM capable of anything, a number of VMs with various hardware limitations and capabilities that target a specific problem space.
(hypothetically, needs further consideration:) an 8-bit VM for processing text, a 32-bit VM for processing images, and a 64-bit VM for scientific audio analysis. The computer the user assembles from these is only as complicated as their problem space.
all of the aforementioned are far from rigorous explorations of solutions. treat the above with a grain of salt.