My guild has just built a quarry for the stronghold and is now focusing all efforts towards the rank 4 guild hall. From the listed cost I can see that is still many months away, despite our slowly growing number of members. At least character growth (strength) is a little better (even for people like me who refuse to pay to win), and just last weekend I got an indication of how strong some of us are becoming.
It's fun to smash stuff that once was a challenge.
From what I've seen so far there are three boss encounters in the stronghold area, and all come in pairs: beholders, pit fiends and undead giants. Our first few encounters with each when we first "arrived" didn't go so well (multiple encounter fails), but as of last weekend all three pairs have been downed convincingly, by just three of us.
It will be interesting to see if eventually, just a pair of us can do the same and eventually - if I can solo all of them. Mind you, that is probably a much farther goal than the rank 4 guild hall. :P