So, Infinite has 6k players on steam concurrently. Maybe double that across the Xbox family of consoles. So maybe that makes for something like 20k if we’re being generous.
The problem with Infinite is multi-faceted. But no it’s not cause it’s Halo. Halo has multiple audiences and communities, most of which have been ignored throughout 343s life cycle.
Forge, Custom Games & PvE/Firefight are all individual communities that have nowhere to go in Infinite.
If the game had those features properly implemented, (Which seems possible by the end of this year, with the exception of Firefight 
) boasting a highly marketed & loud relaunch with an impressive roadmap of S4 - S5 (3 month seasons) and its critical issues (desync/lag/PC optimisation) & technical debt fixed then I believe you could safely aim for something closer to 40-60k concurrent players. Maybe even more across both platforms.
I’m aware it’s a pipe dream, but I was discussing it with my sister and wanted to share.