I believe that to relaunch and encourage users to use WpForo 3, it should have a free basic version (like now) and then a Pro version with all the options (add-ons).
I find having to purchase add-ons separately counterproductive, also because it makes the forum very expensive. If a user wants to spend a lot, they end up opting for xenforo (which objectively is the undisputed best forum today).

I don't know how many add-ons are sold (and, more importantly, how many are renewed), but I believe a Pro license at a reasonable cost would be purchased by a good percentage of WpForo users.