Blocking quotebox spam ≠ full forum upgrade. The current dm issues are definitely more important than that, at least so far.
But if that's the discussion, then I think a complete overhaul of the dm system should still be a priority over a forum upgrade, since the forums are more functional to their current purpose. Moderators should be able to have multiway discussions where the entire conversation is readily readable on this site for when issues that merit private discussion come up, rather than having to take everything off-site. Not that every moderation team would want to do that, but it should at least be an option.
Yeah, not going to lie, the DMs are useful as it's at least a form of communication that every account is guaranteed to have (aside from newly made accounts for whatever reason). Some contact methods are just inefficient to use, and others are, well, twitter. Fixing those soon would be quite nice.
The forums definitely have some jank, but being able to infinitely quote is just a lasting oversight rearing it's head.
More than anything I'd like to get a bugfix for that error where the sense of community and understanding between the staff and users is gone, but at this point I ain't got high hopes for that.