Player numbers are always a good indication of how successful and popular the game is, but it could also be an indicator of good marketing. The tournament registrations, on the other hand, are a great way to measure how much people enjoy actually competing and how healthy the community is.
With that in mind, Evo has just announced that Tekken 8 has surpassed the franchise's record for all-time registrations. What the actual numbers are? Uhm, nobody knows yet. However, given that the previous peak was roughly 1900 players, and Tekken 8 absolutely exploded in popularity, it seems like 2k+ is a safe bet.
Although as a fan, I'm kinda hoping that we can expect at the very least over 3k. It's not a series where you can quickly get good enough to compete, though, so that definitely makes the explosive growth a bit more difficult.