Why can’t the headphones buffer the sound for a second? Why would it need protocol support? I’m thinking something like anti-disk-skipping on portable CD players.

In theory, headphones could store music in a buffer instead of playing it, and then delay playing it by say 2 minutes (or 5 seconds or whatever). Even if existing BT profiles preferred losing quality, you could have BT headsets that pretend to be storage devices and accept file uploads and which then play them after they've been completely received. Ideally though, you'd use one of the BT profiles that already provide guaranteed lossless audio transmission (or develop one if there's none). In a sense, BT profiles are protocols within a protocol, so you can develop almost anything you want (ofc, you need devices to support those profiles too).

Of course, the experience of clicking play on a song and having it only start a number of seconds later is not something that'd sell particularly well, I guess. And then you'd have to renegotiate the BT profile if a call comes in that has to happen live. And switching back to the song will have another big delay.