[Blackwolf]

Don't think it would be a big problem personally. Problems I see are people bypassing the ocean entirely and using Warp Gates.

Unless bringing naval power to the battle has a serious impact on it, people aren't going to waste time trying to drive a 40kph vehicle across the ocean.

It would be awesome if such vehicles could serve as artillery (battleships), and repair/rearm stations for aircraft (carriers). Would be the ultimate raid formation, but I think it would be easier to just go via warp gate honestly. Depending on what the capabilities are, you could make a very effective off shore base to attack from, complete with spawning and vehicle creation.