About forums, I've already done some of those changes... an even more. (I'm writing a long list of new enhancements... I'm slow, but I hope it could be finished soon).
I've uploaded some screenshots to file-storage: Forums Enhancements. For instance, the "reply" button after the message on message-new-reply sample.
About headings for message titles, is possible, just with a "title pretty". I've use bold on titles to highlight new messages (and new responses to messages, I mean, you can see if a thread has news even when it's collapsed)
About the collapse and expand message, I've done in a different way, although I'm not happy about my change, the actual "collapse" function should be replaced (I think) to meet the the main idea is what you said.
I've added a lot of catalog keys, I mean, there are new keys, of course, but I've also reviewed the actual i18n and found a few plain text strings that I've added to catalog.
Another issue about validation, not only on forums but elsewhere, is html id's: AFAIK it's not recommended id's to be only numbers, so, I have replaced id="12345" as id="messsage-12345", and I added some id's to divs that hadn't anyone, for instance, somethink like... id="collapse-wrapper-12345", id="collapse-button-12345", and so on.
