What if Matthias Corvin had had a legitimate son to succeed him on the throne of Hungary?
He tried to make his illegitimate son,
János Corvinus his successor. However, he was too young and inexperienced to rule a state yet. Also he would be even more isolated politically than Matthias: he himself was looked down upon by other rulers because he was not from a royal dynasty, just the son of a nobleman. Now imagine being the illegitimate son of that man.
Like said, Hungary was an elective monarchy, so he could be a king only by the nobelity's will and they had no reason to make him a king. If he bacame a king, he would porbably be a puppet of the aristocracy, as he lacked the charisma and experience of his father. So I guess that would be kinda like OTL with Vladislavus.
If you want him to be a successor monarch, have Matthias living longer so his empire can stabilize a bit more anf
János can pick up more experience.