@Schwieps : There have been no official announcements on specifics relating to new device support or dates as to when such additional devices will be supported.
It will just be a case of wait and see, although the most recent announcement https://community.stadia.com/t5/Stadia-Community-Blog/Stadia-in-the-New-Year/ba-p/13027 did imply that additional Android phones would be supported over the next 3 months.
Tablets need longer time I guess. Google is working on rolling Stadia out for more devices, so might be worth to keep an eye on their social media channels or in their Community Blog here in the forum, in case they announce more devices. 🙂