When I was still in that 'I should write a programming language' stage of career development, I worked on a pretty sophisticated (for the era) mobile app. PyPy was getting quite a bit of press around that time and my brain connected some dots.

One of the ideas I wanted very much to explore is scaling the API, both up and down. For building something akin to PyPy, you might want a 'kernel', a small set of libraries that were available everywhere, and several other levels that include more or different things.

Mobile takes the base and adds a few things suitable for mobile (storage, UI, broader networking). Desktop has a real UI, and then there's the kitchen sink like .Net and Java have.

But you have the same problems you always have with decomposition - if you didn't guess the right boundaries when you built the thing then removing or rearranging bits is a serious PITA. Sometimes I think the best we can hope for is to leave clear messages for the next language so that it doesn't organize things the way we did.