I think that a web UI is impossible, or it would be an enormous contradiction.
The main reason for that is that Sia have as goal to be decentralized, and a web UI would mean that there will be a centralization in one's (or multiple third-party) web server.
A solution to that is Minebox (https://minebox.io/)
Minebox is a NAS that runs a web UI for the user and keeps the complicated things like keeping the blockchain synchronized for it, and it respects the decentralization principle because you physically own the box, that is connected to a decentralized network which is Sia.
Hope I was clear, if not tell me it, i'm not a native English speaker/
The set up around minebox is really sweet. Everything in a box, fire and forget.. nice
..however.. What the world need now is first of all solid and error free sia network ( I think there is a good road map already) and more services around it to really start boosting demand fro storage.
Storage is already there in place in large quantity.
If I buy a MineBox (https://minebox.io/) would it be doing the automatic maintenance? Or do you still have to manually control the state of your backups?
I believe Minebox will take care it for you through its interface and communication with you. I think Mionebox will make everything user friendly and hide all its integration with Sia platform from the users (maybe except the Siacoins).