It's a good idea, but another column in thread table isn't the best thing. Maybe you can make more than one version of this hack (and keep them in the same thread ofcourse).
And maybe you can also keep providing version 3.4 for people who don't like the AJAX feature? I'm using it and I like it a lot, but I can imagine that some people would like to use the original version without AJAX. There aren't any known bugs in it, so I think it would be a good idea to keep it avaiable for download