In my opinion there are already enough tools to navigate and nothing really needs to be added.
The only things I would add, or could imagine to be added, would be the ability to set a marker manually, so that for example in case you log out at Sea, you will remember where you have been when coming back later. Also I wouldn't mind to be able to draw a line on the map and get the info on the course like with classical nautic instrument (don't know what they are called in english).
Finally, if you really want even more, the only thing else to navigate and fitting the game would be a small sextant simulator, hard to handle (as i've heard it was in reality) due to simulated rolling of the ship and and not perfect equipment.... You could use this/enter that minigame or whatever it will be, only at noon and the weather will be considered. So if you are in a storm, there is no chance to see the sun and get your location. And if a storm is gone you have to deal with the waves...
But I firstly doubt that there will be anything the way I imagine it and secondly, and that's the funny point, those complaining about the "lack" of something to get your posotion would try it once, consider it to hard/inaccurate... but those speaking up at the moment for no further tools, will continue sailing without it, while considering the "sextant"app as a nice tool and maybe use it from time to time just for the fun of it.
PS: also navigation inclueds a lot of algebra. Like a sextant does only read out the height/angle of the sun... so the navigator has to do the maths. Oh and to get longitude and latitude you would have to constantly measure the time and watch the sun and simply guess again when you think it reached noon at your location. Compare it, do more maths.
"Congratulations, Lieutenant. It seems we finally found the origins of the Nile. For if your calculations are correct, we are currently sailing somewhere in central Afrika."