I'm not looking forward to re-writing my projects from scratch. I have a strange feeling in my large intestine about this...
The GameMaker: Marketplace/Player are still in beta. So they will go obsolete before they are even out of beta.
I doubt by the time GMS2 is out, they will still want to work on porting to Mac and Linux the 1.x Player, but I could be wrong.
It's a free service, which they provide free out of their own kindness, meaning they can decline from providing it, at any point in time they decide.
I hope my extensions will still work in 2.x. I'm having enough trouble keeping them to work in just regular 1.x updates...