main concept is maybe getting deposits that are not on home isle
with probably sick work times and construction costs

but holding this territory might be held
via constant pvp
or won match
or maybe weakly ladder (longer periods of time)
or just plain pve
i guess there could be many instances of these islands producing different sums of goods.
to give more push for guilds to involve into pvp im not sure how people feel about pvp or pve but im guessing pvp takes more of you than pve so rewards there should be higher.

but then again there could be just one isle for best guild on server which would everyone attack. and try and hold. it.
and we have many more pvp options like capture the flag with maybe 5 guild members and fix number of units or all out guild defense aginst one or more guilds all the time or just some period of time in day.