I'm about 50/50 mobile and desktop when it comes to my internet browsing in general, and while I do not find the current forum unusable or anything on mobile it isn't optimal. If you are moving to a new software system (which it sounds like is the case), then I'd imagine just about any package would include mobile support anyways.
The one feature I'd really like to see implemented is a togglable notification system. You could set it up to notify you any time someone quotes you or mentions you in a post, and maybe even everytime someone posts in a "watched" thread. Every other forum/community I've been a part of has this feature, and it is so handy in keeping conversations running organically.