I have 10 accounts with 8 on the battle.net account. I use keyclone to start them up and just save 1-8 as the email login and 9 and 10 as accounti and accountj. Then I select the account from the pulldown on 1-8.

It's easier to not have them merged at all then you dont have to select them. I don't see the point in having a limit on the number of accounts.