The first thing I'd need is to update the android app so that it uses the newest APIs. There's been some reports of issues with power saving and android 8 ignoring wakelocks. I looked into it and I was never able to fix it (or reproduce it on my device).
Once that's done, I want to unify the PC version and the webapp, a full rewrite using Electron (the android version will keep using java, but it will be updated so that it has the same sound as the PC version). This is especially important for mac users, since there's been reports of the mac version not working properly on newer versions of macos. Apple has always done its best to make cross platform development as shitty as possible, and frankly I just gave up: if someone can fix it, good, otherwise macos can go fuck itself.
Finally, the SINE preset format itself should be improved: it needs better preset descriptions as mthakurr said, support for different types of noise, and maybe more.
Right now SINE just doesn't have enough users compared to some of my other projects to justify the enormous effort of basically redoing the whole project using more modern technologies. If someone wants to do it, I will be 100% available to them and help them do it. The project is fully open source so anyone can try.