You still have an idle graphics card, but you can enjoy the benefits of it from any laptop in your home network. My gaming desktop is wired, my Linux laptop is wifi, and I get 4K @ 60FPS flawlessly.
However, I would prefer not to have to upgrade in the future and offloading the intensive parts to Google would be highly preferable.
No matter how good Google's CDN network is, you can't compete with sub-1ms in-network round trips. There's not really any clever "latency compensation" you can do here.
Even if you rewind state to apply input, which games probably won't support anyway, that still only helps you close the gap added by internet latency. A gap that in-home doesn't even have in the first place.
This may result in a visual glitch, but you won't have missed your target.
Of course, the hardware you have to throw at it to do that quickly becomes ridiculous, unless you can come up with a way of efficiently rendering the multiple versions.
[1] https://www.libretro.com/index.php/retroarch-1-7-2%E2%80%8A-...
That said, I had my Bootcamped MBP with a XB1 controller connected over Bluetooth and any input lag was negligible with the Assassin's Creed Odyssey Project Stream demo.