some soundtracks are just not available on youtube/soundcloud etc so could it be possible to add an upload feature through which we can upload soundtracks from our computer instead of the web
Upload from pc?
That is not possible, it would first require a big volume of storage space to do that, which financially is out of the question and second new features are halted for the time being, due to mishaps of the owner.
You could use a VPN service like NordVPN to view the content not available in your region. If you have YT premium subscription too then you can download and listen to literally everything. Hope it helps.