I could not honestly judge that since I'm not familiar with the code base / project leadership at all. Given the project's reach I'd figure they have that part of the code thoroughly covered by tests and well enough separated to keep maintenance efforts on the low burner.

The linked Google Doc says that usage in a 28-day window was at 0.01-0.03% of users (not sure which figure to use there). Sure, that sounds horrid at first but think about how many users Chrome has, that's not nothing either. Instead of implementing encrypted connections to make their software better, they jump to deprecate yet another protocol. I just find this really hard to grok. How many people used the profiling features of the developer tools in that time frame for example? Not many? That's cool, do we get to keep those anyway?

Browsers are complex, yes, it just would be nice if we could expect a bit more of a graceful deprecation process with better communication. If you don't feel like supporting it, move it to an extension/plugin to separate it and put it somewhere the community can pick it up easily.