Steve
I definitely agree that we do need a migration plan :) We're only just now at the point where web2 is useful to anyone (currently attendees only), which means that this is a great time to start to think about how this can work.
My vague strategy so far is to start adding new features and better admin tools to
m.joind.in and let the community leaders start to use that as their primary version; the masses will follow and we have really excellent support from the community in terms of conference organisers and user group organisers.
There isn't a solution for making signin work across sites so as things stand it wouldn't be possible to link across between the two. I intend to just turn things off on web1 and make really good support/documentation/tutorial videos/whatever for web2 ... we'll do a better job this time and I hope people won't hate us too much for forcing them to change.
Now I've shared my vague plan, does anyone have any other ideas to suggest? I'd like to hear them thrown into the mix!
Lorna