1) Very happy to see the submarines being introduced to the game. This was one of the main things I was missing here since the start of the game. I hope they will provide rich and 'in-depth' interaction with the environment and surface ships/planes.
Also I think all ships should have some counter-play against them - battleships and heavy cruisers too.
I'm happy WG changed their minds and decided to introduce them - It was disappointing for me that subs were not here since the game launch.
Also - giving hydro-acoustic search to submarines - seems like something to consider.
2) Other great set of features would be: more weather effects that would affect lightning, waves, rain, mist, snow, visibility, water transparency and hue etc.
3) The other thing I was missing was more realistic water and wave simulation - and water interaction with all ships - but I know fluid simulations are challenging computer-science topic - so I was not really expecting it to be realistic to introduce soon.
Happy to see game is developing, I hope to see more improvements to make it even greater software.