The only way I can think of is to look at the Campaign volume per server. Right now on console there are 33 of the population blocks filled across all the servers. If one block is say...100 people...then somewhere around 3,000 people in Cryodiil on PS4 right now. Assuming the ratio is 1:1 with PvP/PvE players as well as Xbox players, then 6k total on PS4 and 12k on console all together within the NA server. Again, 1:1 with EU, then 24k on console worldwide.
If I had an actual number of the server limit then the number would be closer, obviously, but that's my guess for console. I know they sold 300k physical copies, and it'd be safe to say that number is equal more or less with digital copies. So I'm guessing is the actual number is around...150k active players across all platforms.
Who knows really.
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