Thanks for the feedback! :)
I think the biggest limitation/nuisance would be the loss of code injection. Everything else wouldn’t change often, or could probably be dealt with. (Is a schema invalid if it doesn’t specify image sizes??) But if a site is basically static** in terms of layout changes and is just getting new blog posts added, then maybe it’d be OK.
**Does this happen? I’ve never had a site that was not under active development/tweaking, but surely it must happen to some people, right?