https://youtu.be/SHaXdWvQHEg
Many, many hours later:
He made this by C.U.B.E. building tool and buildings can be destroyed - unless built offline or in starting zones BUT there will be siege windows (time for destruction) and it should take big number of players and siege engines.
The game is Camelot Unchained, "Dark Age of Camelot 2", PvP / crafting / building MMO by Mark Jacobs. Or you can check it's IGN Wiki for quick intro and more pics + videos. Access now is not too cheap, but beta starts in a month or two (?) and they should have open beta (free tests) in 2017.
Trivia: