One thing that got in the way with the registry for me was that there's only 1 of them. You can't install 2 variants of anything that uses the registry, unless

One thing that got in the way with the registry for me was that there's only 1 of them. You can't install 2 variants of anything that uses the registry, unless that thing uses the registry in a multi-tenant way (and a lot of things didn't).