The iPhone 6s and 6s Plus both have the second-generation Touch ID, which is a lot faster (hate it or love it) than the one in the previous phones. It looks like the new iPhone SE will have the A9/M9 chip from the 6s, but I haven't seen anything about the Touch ID. Is there some technical or other limitation that would prevent Apple from using it? If so, what? If not, I think it's safe to assume that along with all the other internals, Touch ID will also be updated, and they'll use the latest and fastest version in this new 4 inch phone as well.