[Kipper]

I genuinely think naval combat has merit, if the continent(s) are designed right, so that there are some offshore areas which promote it, and some coastal areas which can involve land and sea fighting against each other.

I'm not sure on the wacky new vehicle ideas though. For me, you'd take the formula already set up by the land vehicles:

Quad bike = JetSki
Lightning = Motor Boat
ES Tank = ES Ship

They'd basically be as they are on land - similar if not same fittings and weapon slots, but with inertia, so they handle differently at speed.

A couple of additional variations might involve a larger boat that can stay out to sea and contains an air-pad for fighters, or one that can beach itself like a landing craft, and contains a vehicle and/or infantry spawn.

If you go for a continent that has lot of forest/jungle cover, then it takes deployed galaxies out of the equation (but you can still air-drop from them, or land them in certain open areas), so the spawning boats would suddenly be way more useful. They'd also probably be smaller than a Galaxy so harder to detect; and pack some decent AA in deployed mode.

You'd need to establish beach-heads to set up a mobile spawn near the target, defend your spawn and push out into the base you want to capture (or do spec op air drops / jet ski zergs and take a spawn tower on land with an elite squad).

Opposition would need to secure and hold the beaches; attack landing craft either from the air (risky if they are deployed) or from the sea (still risky, but
less so) in order to defend their base.

You could have fun with the environment too, with some natural bays, high bridges, inland rivers, shallow caves that provide cover from air, etc.