Let me start with we would love to have something like this at some point.
The glaring problems I see with your suggestion:
1. Gammas must retain their incentives to go there. I know currently there are not many but still, simply not having colixum on these PvE islands is not enough. Personally I would only allow T1 buildings to maintain the industrial superiority of gammas.
2. Free building anywhere will go terribly wrong, the same thing will happen like now with gammas. Everyone who can quickly build a colony will occupy all the available space on day one, and the whole feature will be a toy of a handful of players, till the end of days. You surely know that a weekly tax of 1 million NIC is laughable for the veteran corps.
In order to let everyone participate in a totally free system, we would need to have infinite island space to make it future-proof, so this is a no go.
Islands divided into fixed land slots where a corporation can only own one would help, but then alt corps happen.
We could also have an auction system where corps are bidding blindly for two weeks of land ownership. The blind part is important because it leaves a lot of chance for those who don't have much NIC to burn on this. Unless of course big corps throw a LOT of money into it to bruteforce ownership, but in this case it's a very good NIC sink, and it probably can't be sustained for too long.
Auctions then happen in regular intervals and if the current owner can't pay the actual highest bid, they will lose the land slot, and the highest bidder can move in. (With a few days of grace period to deconstruct their buildings.)
This would basically create a market for land, where prices fluctuate based on demand and location. For example locations close to teleports would probably be more sought after, which would drive its price up.
Glad to see it's on your radar. There are some great ideas here to balance PVE vs PVP Gamma. To me the idea makes sense simply to expand the users of what must be a lot of coding. It feels like a lot of work went into Gamma and it's a shame more people can't/won't make use of it.