At that point I'd just make a Patreon (that offers various benefits including exclusive videos not on YouTube) while also monetizing via YouTube ads and sponshorships.
Yes, there is a reason I said "you would need 900 true fans, patrons, or whatever other label you want to give them". I'm not claiming this is a new concept, I was making specific allusions to Patreon and the idea of 1000 true fans[1].
[1] - https://kk.org/thetechnium/1000-true-fans/