That's what "Mozilla/..." already is and always has been, and it obviously doesn't work. All you need is for one browser manufacturer to break the rule and advertise their new feature via something new at the end, and then everyone else who continues to play by the "standard string" rules suffers.

Don't get me wrong, I am not advocating UA strings - but to get rid of them, there needs to be an approach where there isn't a punishment for following the rules.

Hell, I'd be happy if browsers sent a content and platform dimensions headers... so that I at least know the screen size, and if it's in a window, the content size that will be filled.... would make it really nice to be able to do adaptive rendering of the markup.

Even removing"Mozilla/" could break UA detection that uses hardcoded string indexes to version numberz. :(

Opera since 9.0 up to 12.x had user-agent without Mozilla. I still use Opera 12.17 and mostly only Google's sites are broken.

Interesting! I did not know that, though I think many users would complain if "only" Google's sites were broken in browser X but not Y. :)