I agree! If you are under spousal sponsorship , I think it would be impossible to do it online, because number 1, you have to submit not only the forms but also proof of genuinity of marriage/ relationship... and that includes tons of pictures, chat logs, letters from friens/ family, phone bills, rent agreements or mortgage etc... etc.... etc....
But who knows, maybe some day they will offer an online option, this so simplifies processing for them, I'm sure... Just a little bit more scanning

However, there might be some legal obstacles, I don't know, like, original signatures or something........