I kind of think that since he’s gonna be able to be more open about who he is and be able to be with Simon openly he might not want to abdicate (or step down/resign). If he can be himself, being crown prince will no longer feels like a prison.
If you ask me, my personal choice would be abolishing the monarchy.
Lisa gave us hints here but still kept the choices up to a debate
Is it democracy if you have a functioning royal system? Keep breeding heirs? What if your heir wants to marry their same sex partner? If you want to keep the royal system, will you make changes for the bloodline continuation in line with it?
Sure, we will not see a marriage but I think bloodline issue will be brought on the table.
All things aside, does Wilhelm really want to be a king one day? Will he obey the system or change it? Will the system accept such a 'radical' king and the changes he might want (request) to make?