Geforce now just let's you play games you already own (with some limitations based on publisher deals, developer support FWIU etc). And it's just as good as stadia was in terms of user experience IMHO having used both.
GeForce Now runs essentially normal Windows VMs with GPU passthrough to some of their beefier multiuser cards and a custom remote desktop mechanism. There's no special porting involved, it's essentially the same setup, but extra optimised, as what people setup themselves using various cloud providers.
Thus GeForce Now has close to zero porting burden and could just attach Windows Steam client integration.
Stadia didn't have that - I have no idea how it was actually implemented, but someone mentioned that Stadia version of Cyberpunk 2077 was "the PC version, no porting".
Except the Stadia version is the otherwise unreleased Linux port of the game, using Vulkan for rendering (unlike DirectX on normal PC release). It had to use a custom input, sound, etc implementation for whatever interfaces Stadia provided.
FWIW, AFAIK that build also worked on normal Linux with X11 so long as you had Vulkan drivers.
But yes, the big hurdle was that Stadia required a Linux binary, possibly also required Vulkan. Every game they wanted to add had to be effectively ported.
GeForce Now has Windows and various game stores as hard dependencies, which feels like in theory optimizing for the short term and limits how smooth the user experience can be made. But in practice it works fine, and the reduced overhead for individual games maybe is better at least for medium term too.
Meanwhile on Linux, everything breaks every time the distribution is updated. Because they're now using the right XYZ framework and every single app should be ported.
Yeah, although it seemed like the original goal was to make it a sort of “Netflix for games” subscription service where you’d get the games for free so long as you kept paying your $10/month or whatever. Apple has been trying to do a similar thing with their Apple Arcade. Unfortunately the included games were mostly “B” titles, with the exception of PUBG, so you still needed to pay to purchase the good stuff.
I was looking at prices for a new gaming laptop, and realised that it was perhaps 4 or 5 or more years of subscription fees, and that I could just use a lightweight X1 instead. Perfect