1) A notification system. Most usefully to provide notifications of when a post of mine has been quoted and responded to, but it can also be useful to provide notifications of replies to threads you choose to subscribe to, or when a particular 'followed' user posts. (I note there is a 'Notify me when a reply is posted' option hidden in the Options section below each post but there is no in-forum system for any such notifications to be displayed. I suspect the option does nothing but perhaps it triggers e-mails? I'm trying to remember to tick it to find out but this in itself is a hassle.)
2) The ability to 'like' the posts of another user. I see the forum has a 'karma' counter but this clearly isn't in use. Many modern forums even have a range of quick response like e.g. a LOL type emoji response to something you find funny. Some will no doubt say this is totally unnecessary but I think for most this makes forums a more enjoyable interactive experience, meaning they're more likely to stick around and participate.
I'll be honest I'm very doubtful changes like this are likely to be made but I'd love to be proved wrong
. Oh, and more emojis would be an improvement too now I think of it!