I think one of the bigger/noticeable nuisances of current and previous versions of phpBB is all of the page loads required to do trivial tasks. Using AJAX or jQuery or both together for some of the actions performed on a forum would IMO make phpBB take a big leap forward.
Some of the places that I can think of that could benefit from this are:
- Posting - Quick Reply was added but you still get a screen stating that the post was successful. I suppose that by just simply posting up your message would make it "Quicker Reply"...
- Pagination - Maybe the entire page doesn't really need to be reposted to see the next page. This would need a bit more thought.
- MCP Actions - A lot of them could use without having to reload the page in its entirety.
- Some ACP actions - Enable/Disable in several ACP areas comes to mind here.
- Others
There might be some other technologies in the works that can accomplish the same thing but that's up for discussion I guess.