Hey Joss, good to hear from you. I agree with you IF people are using the web, but now that Twitter increasingly own the mobile and desktop client spaces, this won’t be an option.
re. moving to Identi.ca – I’d agree if it was just the tech community, but personally (may just be me), I have a lot of interest in a wide range of people on Twitter, and not all of them would be happy shifting to a more geeky environment. Ultimately, it’d need a “all jump” thing to happen, and that’s unlikely.