Brodgar is a concept that interests me, it offers a playstyle on haven that is almost civilised. Personally I would be very very interested in seeing this place endure. Though, from basic observation, there are a few requirements for this :
1. Active leaders
2. Active police force (to prevent internal raids and some external raids)
3. Support from large factions to deter outer raids
If those 3 things pop up you'll have a successful Brodgar. Otherwise one of the factors above will eventually cause the town to disband and break.