I think the software if anything would be the least harmed by a twenty year term. If you wanted to make a closed source compiler its going to need to be better

I think the software if anything would be the least harmed by a twenty year term. If you wanted to make a closed source compiler its going to need to be better than the latest open source ones for anyone to buy it, so it seems like starting with a twenty year old design and having to (cleanroom) fix all the various bugs that have since been found and modernize the codebase, plus add all the new features needed to be competitive, would be a nonstarter. If you could fork the latest version and make it closed source, then it's easy, you just add a couple useful features and now yours is "better." But if you have to start with such an ancient version and decades of technical debt you didn't even create, it would be a total waste of time. The open source one would continue getting better while you were playing catchup to even release it.