Premature

Well, the merkle-tree-based certificates do work with traditional, non-quantum signatures as well. The bandwidth benefits there are potentially less extreme, but that's a matter for measuring people's actual browsing behavior.

I do see your point, though. Certainly nobody should be adopting a new, purely post-quantum signature scheme without accompanying it with a traditional signature scheme. Luckily, NIST has standardized a set of secure ways to combine multiple signature schemes, so using hybrid authentication and encryption gives the best of both worlds.