It would be nice if MyBB 2.0 made use of some of the Microdata from Schema.org for marking up the content.
Google and various other search engines are giving this specification their backing, so it might be a good idea to get in early. While they don't use the entire specification in their search results yet (if I recall, they use little bits and pieces), it's always possible that they'll issue new updates which further extend what they do cover.
Ideally I would like to make use of some of these for things like breadcrumbs. We may even have it implemented there already actually.
Following the full specification might be a bit much, but it would be a good idea to use it where it makes sense.
Some of the items like Website, Webpage, etc. are a little over the top and don't really provide any information they couldn't already find.
Quite a few of them are actually ill-suited for forums and are more for social networks.
E.g. Where on earth are you going to get all that data about a user? I guess you could theoretically just mark-up the name (and possibly the group title?) on a profile, but is it worth it? A profile is really just a profile. There are even some items which are intended for hospitals, if I recall. Sadly, they haven't given much love to forums. Maybe, we should push forward some proposals on their Github.
On the other hand, posts could be marked up as "CreativeWorks" with authors attached to them. There are various approaches to this like marking them up as a conversation, but an opening post could be anything. It could be an article for people to read, with the responses being "comments" on that article. CreativeWork just happens to be a more generic form of the more specialised items like Conversations, Articles, etc.
It basically tells whatever search engine is indexing that these are "CreativeWorks" aka posts were written by these people at x time rather than it just being a big block of text they know nothing about. Perhaps, group titles could be marked up in those posts, so a search engine is like... Aha, this person's job title is "administrator" and it would give them a piece of information to include in results when someone searches for that user on that site.
The possibilities are endless, although a good portion of that would likely have to be filled with plugins.