Well, it could be a good idea that bitcointalk generate a message from your bitcoin address in your profile and asks users to sign it then access granted once it is verified. However it should be an option and alternative to recaptcha. So when logging you could choose one of it.
Problem?
and it will result in a google car going through a living room... I am sure there are little funny guys answering wrongly on purpose... this is really slavery what they do with those captcha... we waste time, and then they sell our work... what a scam, another one...
that would save your time from dealing with captchas
"signing message with bitcoin wallet" sounds great but can still be automated (robot) and doesn't seem practical for manual login
specially when you're logging in from other non-personal devices, how do you create signed message and paste it?
you seriously need to improve your opsec .