I know this question has been asked a lot before, therefore I will ask in a slightly different way. I know getting economies ballanced would be nearly impossible if you where to add complete crossplatform, so what I would ask is for your save progress on for example PC be transfered to Playstation, but not as a playable character. Rather a sort of "Highlight" or "Legacy" character that you could use to show off stats with and that could unlock the achievements for you on Playstation and Xbox. Again, it wouldn't transfer as a playable character and wouldn't affect the other platforms in any other way other than giving the achievements.

As a player who spent over 1'500 hours on the game on PC I have very little desire to start over again on Playstation to get the trophies

I know you wont give a concrete answer right now, but this was just to give you guys an idea as I'm sure a lot of people who wants cross platform only wants it for the trophies.

Anyways, have a great day!