Swimming is a feature I've really wanted to see in-game since the E3 2013 game play video trailer that aired in the Square-Enix booth.
We can see Noctis here, diving underwater in one shot:
Then Noctis floating above water as he gazes upon what appears to be Leviathan being attacked by battle airships:
The thing is though, when Mr. Tabata was asked about this feature directly, he responded with something along the lines of(and I'm completely paraphrasing here so bare with me) "If we were to implement underwater battles.. The sounds and animations, especially those of weapons, the motions, physics, and effects would all have to change. We'd have to augment them with an under-water theme. If it were just Noctis, it would be feasible, but considering this for the other party members may require additional time and modification. It's not that we wouldn't like to implement this, and we certainly could, but at present there are multiple things that are on a higher priority list and this feature may require additional time to fulfill, however, if the demand is high then we would certainly consider this, or at the very least, release this feature as DLC if it can't make the initial release."
I'm sure the team has, to some degree, thought more in depth about this as we can see here in the progress report #2. It appears that they were about 60% complete in employing the physics of, "sea drift" and how characters are affected by waves; Which also appears to show Noctis moving or floating within a body of water, not just responding to the waves.
Personally, I've always wanted this in, it would add such a major depth of realism and exploration to the world of FFXV. Especially considering that a large portion of the continent is covered in water.
If it came down to just swimming, I'd be satisfied. Underwater battles wouldn't have to be a priority, though they would definitely be a nice touch. Of course that goes without saying.. Mr. Tabata and his team are known to be skilled perfectionists who would rather 'go big, or not at all.' It makes sense why they would be seeking to do much more than just basic swimming.
We still have time to get this to their attention. So that's why I'd love to get the community's response on this and I will try to forward it to the developers if they don't catch wind of this poll already. Where do you all stand on this, would you like to have this degree of water-based freedom in game, and are underwater battles even something of interest to you?
Or do you simply not care either way? I'd like to think I'm not in the minority with wanting to see this implemented in the full release of the game. Even devices that can explore the underwater terrain(like submarines) would be very cool to see. I feel the same way about possible treasures that could exist under the surface, or even special monsters to fight.
If you'd like to see this feature I ask that you please register(if you haven't already) and please vote, everyone. I would love to submit this information to them as quickly as possible and the more people that are for this, the better the chances we'll actually see this in the final product, along with airships.