YO has the same amount of activ player than MMO, still a few well populated servers. Most popular YO Servers are usually heavily modded and with an experienced team in the background.
Apparently the YO Community is very durable, missing out a major update for nearly a year or not having any update for 1,5 years. Both MMO and YO are slowly dieing. For a game that is still in development, the last real update was long ago.
For now, YO is not dead. You can still fill a server with 64 players, as long as you have a good concept. But it looks like, that devs dont care for YO anymore. The good think is, without updates, they cant mess up your scripts anymore, or leaving you a unplayable world database after an update.