As far as i know, their is no any way at all to find out, but i might be wrong.
Also Same with MCC, any way to get the player count?
There isnt really a way. Just infer the data from the Popular list on the Xbox Games Store.
Halo is currently 5th. Above Ark and Madden, Destiny and Fallout (At the time of writing). The ARK devs gave an interview to GS once where they said their peak population on console is roughly 105,000. So just use that data to infer Halo 5’s population. Peak populations generally happen in the evenings, but keep in mind it is a Sunday today.
They would never tell us…not unless it was a huge number and they could brag. They would be too embarrassed to actually tell us. Or they would somehow be vague about it like when they said H5 has the highest player retention ever