Firstly the minor one. Restrictions on transfer is what allows us to pick up ridiculously cheap old/good games. Cheap (humble bundle or a steam sale) or even free (you happened to be on epic and pressed a button this month). There are already 'some problems' - but these services will be killed off.
Major concern I have is that every game will "become a subscription service". I love my stack of steam games sat there to be played whenever I want. This is available as I currently have a perpetual license for them, and this is possible as the current market sells many many many more of these licenses than there are people concurrently playing these games.
i.e. If licenses were made completely transferable, then gaming would become a 'market' like some weird global Uber.
EA creates 100k licenses for a game (and the back-end support for it), if > 100k people want to play it the price to play per hour goes up (or they release more licenses), and if less it goes down they cut the price... ...again I'm OK with the model.. but not how it impacts how I see 'my games'
My real objection being that this won't magically become an open market, it'll become subscription hell. EU can say something has to be resellable on Steam, but the industry response will be to "not sell on Steam" - and create endless separate markets.