After applying https://gerrit.wikimedia.org/r/#/c/376135/ and parent patches the Minerva skin will work without the MobileFrontend extension, however it will throw JS errors and not be fully functional. This is good progress.

The next goal would be to get to T144402

My plan to solve this would be to conditionally add an external dependency to the RL definition for the rendering library. This will be a compiled and versioned version of the mobile.startup module, but to get to this point we'll need to make some changes to prepare for that.

Currently, given we organise our ResourceLoader modules by feature, the following errors are thrown:
Unknown dependency: mobile.betaoptin Error: Unknown dependency: mobile.betaoptin, mobile.toggle Error: Unknown dependency: mobile.toggle, Unknown dependency: mobile.watchstar, Unknown dependency: mobile.startup

If we can reduce this to:
Unknown dependency: mobile.startup Error: Unknown dependency: mobile.startup - this means we only need to swap out one module. This will be a lot easier.

I am following T158980 and T167713 closely as they will both help with this initiative.

This also opens the doors for rebuilding the entire library using a different framework/library e.g. OOjs UI / preact.