If you head over to the TestLive forum, you can see the update currently being tested which includes (indeed, focuses on) the Thrall Management stuff:
While this doesn’t say anything about when the limit will be activated as such, it will be some time after this update rolls out to Live servers only - Funcom said as much a while back, ie that they wouldn’t activate the limit without first giving us the tools we needed (specifically a counter).
I assume from the tag you’re on PS4, so you can’t use the TestLive product yourself (unfortunately), but the post I linked has lots of info at least.