Except retail and Warmane are two completely different business models, and cannot be compared in any form.
Retail requires a subscription to play the game. In other words, each "multiboxing" account, requires you to pay £10. This means that:
1. On retail there will be a limit to multiboxers since money is finite
2. Retail support that model because they make money from player subscriptions.
There is an upper limit to how many characters you can play (e.g. to play with 10 characters simultaneously on retail will cost you £100 per month), whereas Warmane is free.
In other words, you can create 1000 accounts on Warmane as a multiboxer - for absolutely free, whereas Retail this is not possible. Plus, there are disadvantages:
1. The more "multiboxers" there are, the less stable the servers are
2. "multiboxers" inflate the population; in other words, if there are 10k people online, and 2k are multiboxers, then 2k people cannot interact or communicate with anyone else on the server, which negatively affects the player community.
3. It isolates player communication; if they can solo a 10-man raid with multi-boxers, that would not ordinarily be possible, then they are giving themselves an advantage, since that level of raid communication will not be necessary.
Post-Edit:
The only way Warmane will change multiboxers is if someone abuses the system; i.e., cause instability to the realm, and being forced to cut down on multiboxing. So, if you want it to go, you have to create a lot of multiboxer accounts, and cause realm instability.