I would like to see stats about which games are being played most and which games are being sold most. It would help with multiplayer fans. it would help novices with buying the right game. the list is bound to grow. SO can all the games be sorted by sales ranking.
Google doesn't officially release these statistics unfortunately.
https://stadiastats.gg/ could be a good place to get an indicative number, but that relies on profiles being public which is probably a relatively small portion of profiles as Stadia defaults profiles to be private unless changed by the user.
Eventually when the platform grows and the user base expands we might see those features. They are probably focused right now on bringing the service to more locations and approving the overall usability and ux of the app and website.
I would like to see those features implemented, tho.