Krikooks - all your points are valid, but nothing that cannot be dealt with:
a) in fact there are no real rewards for defense, therefor developers should came up with something
b) regarding flying and other points - there could be something like daily 'siege' (in fact there is nothing like that in system, at least yet) that will pretty much point to current targetted faction boss. This could work like events, something they have started with 5.3 (Barrens) with addition of realm-wide notifications.
Again, as i stated before - the advantage of such events (sieges) would be making our hands really busy without much development effort (most likely needed for Whitepaw's idea) - and it will pretty much be all about lore.
Alternatively, providing zone suggested by Whitepaw is also some kind of a solution, this one would of course automatically scale iLVL (like in Guild Wars 2).
What i don't like about this alternative idea is instantiation - for me its all about encapsulation that makes everything artificial and substract a lot from final form (just like soulbounding did, which in mine opinion has slaughtered real MMORPG experience, but this is OT i guess
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