Would be a pretty cool little addition that wouldn't take that much time up. The champions that don't have one just don't have one yet, but I'd love to hear Draven's theme when looking at his spells, or his lore. Or Darius', or Rengar's, etc.
Because most champions don't have one. Login themes are a relatively recent occurrence.
Not all champions had a login theme
I bet a smart programmer could make this possible as a third-party addition, similar to how we used to have custom item sets before they were official.
As for Riot implemented? Doubtful.
Regardless of whether or not every champion has one, I think it would be pretty cool. Probably wouldn't autoplay it though - just give us the option of listening to it.
Why not play the login theme? Because that requires that all the login themes be either stored on the user's computer or routinely downloaded from Riot's servers, which is some seriously unnecessary bloat.
Since LoL is a free to play game, it is important to ask yourself this; When adding music for every champion, how much will they gain from it, and how much will they lose from it? Of course adding all the + making new ones for those who doesn't have + adding to server and stuff will cost $$$. If it costs more than what they will earn is more than there is no reason to add it. Unless they have so much money they don't mind polishing these things.
8/10.
There's a bunch of good stuff in the login splashes that is lost to history. I've never even heard some of it, as I started playing IIRC when Jinx was released. +1, good sir/madam.
