Just a thought:
Maybe this "lovely island" could have some treasures listed in each province description, that would incentivize individual players? Particularly those in lower leagues. For example, Something comparable to Crow Nest rewards (including diamonds) plus 2-25 unattached rogues to replenish troops. With % chance to win during each battle, while guaranteed all if whole province conquered?
That said...
Did not Inno say back in June that GBG would have similar weight on guild rankings as GvG?
I believe GvG accounts for more than 80% of the total ranking for some top guilds. The remaining 20% comes from guild level obtained through GE, HoF and possibly other activities (I do not recall now). At least that's my limited understanding how it works.
I may be wrong but I do not think GBG affects final rankings like GvG. I think it is more like GE, that adds relatively little...