Hi Sahil, welcome!
The stingray project sounds very interesting! I see that you posted on GSCO gitter, which is great. As Tridge said there, Ardupilot supports submarines, so talking to the Ardusub lead maintainers about a possible GSOC project would be a great way to start.
Also be aware that you can submit several Ardupilot GSOC proposals, if you have ideas on more than one project : Google's official position is that up to five proposals can be submitted. That said submitting more than 2, possibly 3, is a bit risky, as Google tends to frown on too many and would rather have fewer high quality and detailed proposals, vs say 5 that might be too general and not as good. In other words depth is preferred over breadth, so is quality over quantity.