Planetary Assault: based on the first BFG. both teams would support a ground battle happening on a planet by providing orbital strikes, assault actions, sending fighters, bombers or assault boats.
Unlike the first game where if you didnt realized a certain amount of orbital bombardments you would lose the match, in this new mode there would be a score board with an estimate of the ground forces (just like with troops on ships, but bigger), both sides would start with a high number of forces which would gradually decrease over time. on the battle map the image of planet would be shown below with an "holographic" overlay on it indicating lines that separate the enemy controlled territory and yours, with some additional pockets of allied troops in hostile territory.
During battle you would occasionally be prompted with areas where you could send troops by performing boarding actions or lightning strikes anywhere to drain more of the enemy forces or boost your own, with lightning strikes better used as offense and boarding action better at defense, but you would still be able to deploy them anywhere else at anytime, but then they wouldn't be as effective as if they where deployed in the designated areas.
Orbital strikes would follow the the same rules of effectiveness and only ships of the line can use them, with battleships doing some extra damage. For an orbital strike to happen the ship would have to stand still for a certain amount of time on top of enemy controlled areas for it to shoot.
Interceptors/fighter squadrons would be used in defense and can intercept the opponent players bombers, while bombers and similar would be used in the offense, assault boats and similar would work just as the other two assault actions. to keep track of how many bombers and fighters there are in the planet it would be good to have an UI showing how many of them where sent down, or an estimate of their power since squadrons from different factions would have different strengths and weaknesses if i'm not mistaken.
And as a possible suggestion, but i'm not sure about it: ships that can be scuttled can instead be sent to crash on the planets surface but they would also damage your own forces.