I'm not sure I want that in the core to be honest but I suspect it won't be too hard to make a plugin for it if that's what people want.
And, it probably won't speed things up, actually. The signature is still only processed once per user, you then have to have some logic to figure out whether to show it or not, which is an extra check per post, doubly so if you're doing it via a plugin because this is a little overhead there, followed up by the fact that it does actually limit what can be gzipped anyway. Needs testing but I doubt it would actually save bandwidth in the long run, and it may even end up costing more bandwidth in some cases.