How it will work will depend on how it is done.

If they made new cities for realm versus realm
we could A just have that part of GWF and you are assigned to that city or a normal city, the same way if you have to defend multiple cities now
or B have a separate event for those cities.

if they were to just make some of the current cities server wide, then that would be just part of GWF.

BUt I really feel something needs done on servers 1-10

Some realms have lots of guilds some realms really have 1 guild.

If the cost to jump realms would be lowered maybe that would change. Just offering an idea and my opinion, and encouraging others to do the same.