You have the right idea. I want to note that, in a sense, the program would partly be written in the specification language with which ths VM is defined. One could use English - probably OK, though English has shifted a bit in the last 100 years (is it shifting more slowly with the internet, or faster?). And you can use mathematical notation, which has also shifted, but more slowly.

That helps with porting, so it can run, but the question of maintaining the software remains (changing it to meet changing circumstances and needs)

- Is it better to totally nail it perfectly, so only known aspects need to change? (A bit like your VM approach, in some ways).

- Or make it minimal, simple and clear, so the core can be preserved, modified, even rewritten, without losing the basic idea of it?