The primary culture of Transylvania at the start of the game should be Hungarian. Then, depending on which way you change your main culture:
a) Hungarian culture: allow Transylvania to form Hungary if doesn't exist.
b) Romanian culture: form Romania if Transylvania has the required provinces.
They're Hungarian in game and see themselves as Magyar nobles, the provinces are even Hungarian, It seems totally right for a Hungarian Transylvania to reform Hungary if it can pick up the pieces. If it somehow culture converted to Romanian then it wouldn't make sense.
(Mostly) Agreed. See my proposal above.
Yes, this is totally true the rulers of Transylvania were mostly Hungarians and other catholic classes because there was an act that required one to be catholic to rule over a domain, and since Romanians were orthodox (which is not even represented in the game) is why they were ruling.
And it doesn't make sense to say that if they noble rule they would form, to start with in order to get an independent Transylvania you need the people to riot because they don't want Hungarian occupation, so they will never form it back just because they "accept culture". It would never happen. Transylvania cores will always riot if under any occupation except Romanian.
That's a purely nationalistic point of view. We have no proof that Romanians were a majority in 1444. We don't have proof that the Hungarians were a majority either. What we do have proof is that there were only a few Romanian nobles in Transylvania in 1444, the vast majority were Hungarian, German, Szekely. The revolts during this period were of an economical nature: Romanian and Hungarian peasants versus Hungarian, German, Szekely nobles. A strong Romanian national conscience and identity appeared after the end of the game, so it's not extremely relevant - regarding revolts in Transylvania.
Transylvania in the game's time frame was a Hungarian led remnant of the former Kingdom of Hungary.
The proper thing for Paradox to do would be to:
a) add 1 German province in Transylvania
b) change 2 Hungarian provinces to Romanian provinces in Transylvania
The rest of the provinces should be Hungarian.
The reasoning behind this is simple: there are many other similar situations where the province actually has the culture of the majority population, not the ruling class. Transylvania was always a mixed-population region and it is incorrectly portrayed in-game because it's so homogenous.
Examples of similar territories which don't have the culture of the ruling class: Rhodes (Maltese rulers, Greek population), Cyprus (French rulers, Greek population), most Ukrainian provinces (Polish/Lithuanian rulers, Ruthenian population), etc.
Anyway, most of this
off-topic so we should cut it short.