I use Plover as my keyboard layout full time. I'd be happy to answer any questions you have about it.
For competition, I'd point out that Intersteno allows typists, stenographers, and voice writers (Dragon) to compete in certain events together, and also separately.
As long as there's a way to self-identify as a stenographer, seems like it would be reasonable to split leaderboards to still allow individuals to race amongst each other.
And yes, there are fewer stenos out there. I just posted the game to the Plover Discord. Excited to try it soon!