There's a related proposal for Compartments and Module constructor is a prerequisite to that. A shim for the entire thing exists, with lockdown and Compartments isolating code:

https://github.com/endojs/endo/tree/master/packages/ses

https://github.com/tc39/proposal-compartments/

It has usage already, eg. metamask snaps

Realms look really amazing. I'm going to keep a close eye on this. Stage 3 sounds promising.