We have seen a couple of job vacancies a number of months ago for roles in Sports Interactive. Today as part of their website redesign a number of jobs have been added. One of these jobs was for Graphics Programmer and the job listing mentions Stadia.
The quote in full is :-
Football Manager ships on Windows, macOS, Google Stadia, Nintendo Switch as well as iOS and Android. We are always looking at new platforms so there is plenty of scope for an interest in a particular technology or platform.
This would seem to indicate that Stadia is there thoughts going forward. The next version of Football Manager could become a big seller for Stadia as the platform is more mature and everyone will be able to play if/when it launches.
However it looks like we may not hear anything about the release soon