Some friends and I have a server going with 15 or so people, 5-7 of which are regular. We have a settlement, have branched out a bit, and recently killed Bonemass, to give you a sense of where we're at.
We can definitely kill those bosses again if you'd like, too, as we've found a number of spawns.
If you're interested/want to know more, send me a message over on Steam: Bro Sot
May Odin shine upon your travels.