> What is the procedure/convention for superseding this directive when something supersedes USB-C?

I believe the EU are saying they'll keep up with new standards as they come in. The problem I see is, how can a new standard come in if nobody is allowed to use it. Its a chicken & egg problem, the EU will allow new standards as they're used, but nobody is allowed to use new standards until the EU allows it. Thats aside from the obvious problem that the EU isnt exactly famous for its speed.

The only ways around it I can think of is either if new standards become popular in markets foreign to the EU, or if some company decides to add both USB-C and USB-D to their device, which in a world of needlessly removing the headphone jack I cant see happening.