I would like to suggest that the Stadia business team explore something like a 'custom Humble Bundle'
A custom bundle targeting the Stadia platform only
This can deliver broader exposure for Stadia Platform to the Humble base, and 'for a good cause'
If you wanted to make it really compelling and broader the user base add tiers:
1) Game selections outside of the PRO model
2) 1+ Month(2) Stadia Pro
3) HW option: Controller/Chromecast ....
4) Existing Pro subscribers can gift the +1month or duplicate games to their friends
Regards
Lucanor