-Land Ownership/ Claiming: (MC/ Forge) There is an older Bukkit mod called Factions, and now also iFactions that allowed you to do this and could serve as a point of reference. However for what should be needed to accomplish this first part, considering that forge seems to now have dominant share of the mod community. The, entire mod should have to pretty much be rebuilt from scratch, to emulate its functionality in forge. This function should have a clean GUI/Admin GUI and simplified-minimal "claims" Voxel map. (The map could serve as the basis for your interaction/claim GUI, Opis or Journey Map would be a good point of reference.) As well as few in game items to improve representation of/with the the claim. (I can go into greater detail on those "items" or other functions if there is interest expressed.)
-Challenging Claims by Air: (MC/ Forge/ MC Mod/ GoI/ Steam?) Create an add-on to the above mod that allows players to challenge one another to a GoI private match for the claim. The next time both/all (min one per side) players are online on the MC server with an open challenge, GOI Launches into a Private match. This means that every party or player on the MC server with a claim is fair game, configurable by the server admin. (My opinion on this, and I can not stress this enough, is that GoI should not specifically be needed for everyone on the MC server. As a configuration example; A claim owned by player/party not identified as/with GoI, would be at the mercy of a circumstance controlled by a hostile entity. (Elements of gameplay such as this, that affect the game need to be clearly represented in a GUI for it to be understood by all parties.))
Additionally an executable would be recommended for easy GoI setup/configuration, for the ease of the end user. What is required, is an interfacing script to place both/all MC players into a match. Then, the ability to record the outcome and carry that result back into MC. (This will need to change when Muse updates GoI but can transcend MC versions so long as the mod's input-output needs remain consistent.)
The outcome could range from loss of access to block manipulation, a claim ownership change, etc. again, should be subject to configuration by the server admin.
-Ship Construction & Mooring: (MC/ Forge/ MC Mod) Building off of the Claim system. Create a block and item set to allow Minecraft materials to interact in a way to allow "GoI dirigible" to interface with a "pier" for the purpose of Travel and Defense of a claim.
While not specifically needed for the completion of either of the above mods, this for most MC players especially for the younger crowd, will serve as the "meat and potatoes." Its not, but does add a lot of flavor to the mod set as a whole, should this step be accomplished, the "challenging claims by air" and this module should be combined.
What do I mean by building a block set, and how will this interact?- (I will attempt to break it down into two sections.)
-Travel- Believe it or not, this can be the easy one... But it doesn't have to be. This can be achieved in two, perhaps more, ways, first and easiest is connect two sets of points (the helms of a set of goldfish 550m apart, for example) in Minecraft and simply let the player TP between them. If this is the route selected it should come at a considerable cost to the player by consuming coal/charcoal or another power source like EU, MJ, RF, AE, Bar, ect. (There is a pretty good framework already with universal electricity.) It just needs to cost enough to make it not devalue other mods it may be paired with, that offer a fast travel. (5 to 30 coal per 200 blocks traveled in my mind seems to be in the appropriate range for cost, which is lower then IC2 but higher than most other tech and magic mods.)
The obvious hard way, that has been attempted and failed more times under more names then I have fingers, is a working “airship” flight model that won’t crash servers or clients. What I consider the "right" way is a bit cleaner, if less exciting. Again use a fuel source "X" per "X" distance traveled, and two coordinates attached to a block, but make the ship travel in game emulating the work found in Archimedes Ships, Metaworlds, etc. in a more controlled environment. Players would select in their GUI where they want to go, the ship goes to the build height, fly's to the destination and lands. Its not letting players fly themselves around in game, which a lot of people (myself included) want. However it does add "airship travel" to Minecraft.
-Defense- This is the more interesting portion of this mod, that can be approached in a number of ways, I can again get into if asked. For a number of reasons, my preference here would be to create a custom crafting table, and at minimum, the need for a few machines…. Something along the lines as a “lathe” and “Cast.” You also employ an easier method and use the standard 3X3 and furnace with the ability to function as an addon to something like Tinkerers Construct, employing recipe overrides and piggybacking off the popularity and functionality of another mod.
Before I get into the aforementioned "crafting table" I need to explain how this idea flows in my head, and thus work’s as a package.
-Claim land, start a base, build a pier
-Build a ship, (3d model or multiblock, doesn’t matter) assign it to a pier
-(optional)Build a fleet of ships for defending the claim and attacking others claims.
-For each person in the faction that goes into battle as a captain put a ship as a wager on the outcome.
-if a loss, have the pier destroy the ships, if a win the winning side keeps their wager
-To have a claim under contest the pier needs to be empty.
The custom crafting table would allow you to use the same parts, arranged differently to form a class of ship. Reason being is you would probably want a Gali to cost the same as a Squid when you may take a Spire into battle. Its not as though I don't think the ships should have a cost weight, Its just that making your GoI interfacing Script dictate the ship, much less a load out is FAR too intrusive without first party support, and thus more than likely out of reach.
You could weight the cost difference for additional functionality.in MC but again there is a level of balance that both communities expect.
The ships should be expensive, enough to not want to lose, but cheap enough to wager with, using the mod as a stand alone. 40-60 Iron, 10-20 gold. 50-60 redstone, lots of Wood, Wool, some Coal, few diamonds. As for crafting them in this “table” I picture it as being a multiblock structure that you can assign villagers to, more villagers greater cost of currency (probably emerald) Less villagers, more time involved. As an example it would take 1 villager 2h to build a ship him/her self for 10 currency. Or 30 villagers 5 minutes for 50… I don’t recommend using those numbers, but it gets the idea across.
If you made it this far, thanks for reading. Its a bit long winded, sorry about that. I have been sitting on this idea for almost 2 years now and haven't had the time to pursue it, I post this now hope that someone does.
(Side note, should Muse want to pursue this first party let us know so we can throw money at you. (Donations for a respected modder is fairly common))