There’s not only the user’s angle to take into account here, but also the developer’s/mods/admins of the system. Whilst, as a user, I’m perfectly fine with how it works (despite knowing areas of clear native improvement), and will possibly dread the change when it comes, simply because I’d have to change or scrap thing I do with the data, the initial quest for a change in the forum software was motivated by something along these lines:
The forum's software has proven to be insufficient for our needs. In particular, the general architecture of the code is both insecure and difficult to modify, and the moderation facilities are limited. Therefore, the forum is accepting bids for the job of delivering software that meets the requirements listed below. <…>
Ideally, what I'd like to get from this project is software very similar to SMF on the outside (similar features, fast, etc.), but with code that is clear and secure, plus a few extra features that SMF doesn't have (mostly moderation-related) listed below.<…>
The above referenced post (see the complete version) depicts requirements, but also highlights some seemingly major SMF problems. The above shows a will (at least then) to push things into constant evolution, whilst encountering drawbacks in the software that likely led to investing a bunch of time into reaching a stabilized version little prone to big changes or improvements.
It’s not really a Boolean question of it being broken or not, but rather more on the cost of opportunity the current software represents in relation to having a much more customizable, secure and dynamic evolving software that could benefit the forum on all fronts (user, programming, admin/mods, [advertisers]).
Of course, something’s clearly gone wrong along the way with the new software, likely time and over again, and I’m sure that, were it to be ready today for the migration, it would require a breath-taking amount of time to kick-off, supervise, correct and evolve over the following months, all of which require setting aside ample available time and resources (be them prime or delegated) to embark.
Side note: I still believe that the Forum is rather much more than a software per se, and would likely need to be accompanied by some though towards the strategic side to factors such as placement, user attraction, user engagement, and so forth.