While the rest of us wait for an invite... you can DIY your own streaming service using your own PC. I stream games to my phone and I have a Razer Kishi. Pretty great experience. If you're on the local network with 5GHz, there is almost no noticeable latency.
Hosting from your PC can be done...
These are the options currently: https://www.nvidia.com/en-us/geforce-now/download/
Can't run it on an Xbox currently, but you can play Game Pass games now, via the service on a PC/Laptop/Phone
Seems the sign up/join now link only works for accounts that have been invited to the beta.
The link though, for anyone interested: https://www.rain.co.za/nvidia/join-now
This is the link given by the GeForce Now app, after signing in with your Rain account.