I would be curious how that will work with anti-trust legislation. At least currently, there's an argument that Sony does not prevent people from buying games from other sources, or other publishers from publishing physical games for their consoles.
That's no longer the case if they switch to a purely digital model, since they become the sole source of all the games on PlayStation, and have unilateral authority over them. The only place you can get a game on a digital model is Sony.