> Making a future version of C (as an example) unable to build those code bases is effectively branching the language, in much the same way (although probably to a lesser extent) than the Python 2 versus Python 3 split. If C compilers fully support the old version of C, everything is probably reasonably fine; even though the language has branched, old projects can continue to use the old language forever. If C compilers start deciding that they want to drop the old version of C because it's been a while, we are not so fine.
I just don't understand this fear that compilers are going to drop support for C89, like there isn't tons of this code around. Just because X11 is going unmaintained that doesn't mean compilers will drop support for C89.