But back on-topic. Unlocking them due to the Vassal limit being too low/punishing seems like a terrible round-about way to deal with the actual problem. Which is not that they are locked in the first place, but that the vassal limit needs to be raised in SWMH to compensate for the increased number of provinces. I will definetely make sure that we start a discussion internally in the SWMH team about this, no matter what you come up with for SWMH+EMF
Fair enough. Do keep in mind that the increased number of provinces only really ought to affect the vassal limits of dukes/grand-dukes heavily. Above that tier, duchies rather than counties are the units consuming the available vassal limit, and the number of duchies in SWMH, while also increased, is nothing like the +50% county density of SWMH. For emperor tier, the kingdom density is also slightly increased (particularly for places like the ERE, though) but not enough to warrant significant changes in the vassal limit.
I think the approach of reassigning de jure structure by event (quite a simple thing to do, but don't do it quite like Meneth does with the Portuguese/Leonese/Catalan de jure expansion-- I can consult, if you like) is promising, although it's more work. You'd need to keep some titular titles around that were unlocked and then swap them into the appropriate de jure places as the empire grew. Could be quite a bit of event logic to do robustly, so I'm not sure if that's really SWMH's kind of thing, but anyway, I'm around to talk about this if you're interested.