I honestly don't really see anything to try other than what Xbox has already tried. Growing usually means removing any possible barriers to playing. Cheaper system removes a barrier (Series S). No system removes a barrier (cloud, firestick). Not having to buy games removes a barrier (Gamepass). Integrating cross purchase and cross save across PC or console or cloud removes barriers. Put games on a sub to try and expose people to new genres they aren't used to potentially expands the audience. But it's not really playing out that way, so I can't think of anything. Only other thing to do is just keep expanding to other parts of the globe that aren't really playing games at large levels, which is why I don't predict it expanding. If it does expand, it'll be along one of the paths already laid out above, only Xbox was too early and someone else will do it like Netflix.
The other big barrier is input complexity , which Nintendo and mobile already simplified as much as possible. No controller needed for Wii, or mobile. Xbox already tried Kinect for the same reason. Everything to expand has been tried, and it's not happening easily. The last great input complexity reduction will be Augmented Reality. That will possibly be easy enough to get some new people. Only possible way to get simpler than that is a neural link.
Best thing I think is to just put your games on everything. I genuinely think even Nintendo will be strongly considering it in the future because console sales aren't growing. If Nintendo made a play for a sub cloud service, they have enough IP strength to maybe convince normies to give it a shot. The Mario movie is still in the top 10 on Netflix.