So currently the total war method for any game seems to be when two armies meet on the ocean, they decide to land on a nearby island and duke it out there. Weird, huh?
Now I get without proper naval combat, that's the only way they can have it (as before, it was just auto-battles which could often screw you). But I thought of a solution: the two armies will fight on their respective ships as boarding battles.
The idea would be the scanerio is one ship got close enough to set out gang-planks or such to sic their units on the other. This could create a whole new battlefield, as the field would be between two, potentially different styled, ships.
In a hypothetical historical game...let's say empires...we could have a Spanish galleon and a British frigate and the two armies are fighting on both ships, as they cross over the gang-planks to conquer the other.
This gets a little more complicated in a fantasy situation, like Warhammer, but that can be alleviated by the fact the ships can be designed to be larger to hold their massive armies and such. And it would make even more fantastic contrast, as we could have say a dwarf steam ship attacking a dark elf black ark. We'd see the Slayers jumping onto the black ark to fight with the hydras and black corsairs. This would definitely give the designers some new things to work, as we could see the fantastic ships of WH in fine detail.
This idea also could apply to a theoritical 40k game, as it would explain off what happens when two armies meet in space (Instead of landing on some random planet that just happens to be floating nearby, lol).
Ideally, the best end all solution would be to have full naval combat where ships would also be shooting at each other and we'd have special units for battling on the sea in a fantasy scanerio. But as naval combat is a whole different beast to tackle, this would be the next best solution until it could be worked out at least.
Now if this was to be applied, I honestly would see it in a whole new game or very late stage dlc if it was applied to something like WH3 (Getting more important stuff out like faction and lord packs as well as faction fixes of course).