When the sender and the receiver are both online it makes no sense to use a server as an intermediary storage. If the file was directly transferred from one device to another it would be much faster, without size limitation and confidential.
This is feasible using WebRTC (Firefox and Chrome). Our webpage shows how it could work (Takeafile). We are willing to integrate our project (source code, team, brand) with an open community of users. Is it interesting for you to explore this path?