It would solve so many problems for many people that simply don't like certain schemes. Let's take me for example. In an all separate league system I would search Opponents for Roper, TTRR, Elite... although I am pretty good at bng I don't like it that much. It's no always a question of skill. Most of the time we play to have fun, even in league games. I would avoid Shopper/WxW and Hyst. Not because I can't play them due to lack of skill, but simply because they are boring to play in my opinion. And every individual has similar schemes that he/she doesn't enjoy playing. I also enjoy playing against people that enjoy the scheme as well, sure once in a lifetime it's fun to see your skills completely overwhelming your opponent, but that's a short fun experience. (TTRR vs. Chicken for example

) No, I enjoy the high level competition between 2 players that enjoy the scheme and are willing to get better at it. People that are fine with all schemes obviously have no problem with current all-in-one packet. But I am sure, and this thread proves it, that I am not the only person that dislikes at least 1 scheme in Classic League.
People that get into playoffs with their favorite scheme are also more likely to get their playoffs done faster, at least I would assume that based on my own behavior.
@ Chakkman: You can search for all schemes, it's not hindering you, why would it?

If we both would be agreeing to play TUS games I can still offer you my Elite, TTRR and Roper willingness. Why would I want to play vs. you in schemes I don't enjoy, makes no sense.