As Kovid said, anything is possible. I have the code to sync reading positions between my calibre library and my two Kobo devices for sideloaded books. The non-sideloaded books do it via the Kobo servers with a "silly scheme". And I agree it is silly. I can sort of see why someone would think of it, but in the long term, it isn't that practical.
What Kobo uses for epubs is something that I think is based on what ADE uses. I have thought of converting this to what the calibre viewer uses, but just haven't had a real need. If I do it, it would be mainly for the challenge.