Oh, well. Is there any sort of suggestion box/thread here where we can submit ideas to the OpenXcom developers for these sorts of things?
Until TftD is all done and moddable to the level the devs are aiming at, I don't think there is much else you can attract their attention with. Maybe Yankes with his OpenXCom Extended, as he seems to be the most open to implementing new things instead of recreating the originals, but that seems beyond what he usually does.
As I mull it over, actually, it seems to me that any self-respecting X-COM commander isn't going to hand over a base just because the host country defected and called "backsies"; and, since said country is cooperating with the aliens, they would just deliver the coordinates to their new bug-eyed overlords anyway. (Besides, I suspect that a dreadnought USO full of Lobstermen would pose a bigger threat than anything that the Icelandic Union military could come up with on its own.)
So the best way to represent that, then, might be some way to ratchet up the frequency/strength/number of terror units for floating base attacks?
That could work, yes. But remember, XCom fights aliens. A self-respecting XCom commander might not want to fight humans. When an army of humans from a legitimate government shows up at your door, even though they are less scary than lobstermen, will your aquanauts be willing to fire on them? Enemy Within and XCom2 shows that XCom is willing to kill humans that are integrated in the aliens' system, but at that point, the army (and even the government who just signed the pact) isn't yet.
And even if an icelandic trooper isn't much of a threat compared to lobstermen, a country can marshal thousands of troops supported by tanks, artillery and aircrafts. I'm not sure how well an XCom base with ~50 troops, and 3 crafts that can't shoot outside of water would hold up. It's a typical case of "elite soldier trumped by masses of crappier ones". They win in attrition, and a basic rocket launcher can still hurt.
Anyhow, that's a case of different "head cannon". I don't see the XCom conflicts as a typical fantasy-like 100% good and evil fight where if someone is your enemy, they are absolutely evil and deserve to be destroyed. The aliens, yes, but the humans that side with them.. It very much depends on whom.
If XCom starts fighting governments, does it not then become a threat to human society as well and worthy of being terminated? Why would 1 XCom commander know better than all of the world's leaders agreeing that XCom is over? To me, the only continuation that is acceptable after official termination is the kind of guerilla war shown for XCom 2.