Honestly honor farming doesn't accomplish much, you can buy certain tradeable materials with it, sure, but in most cases the time cost compared to some other kind of farming seems like it would be a waste. How profitable it is changes vastly based on expansion as well.I'm not saying WoW is a bad example and it probably has a point over some other online games but it has had and probably still has many kinds of ways of multi-account abuse. You can use your 2 accounts to farm honor in many ways including killing your other faction character(s) with your character(s), going to the multiplayer battlegrounds and forcing the other side to lose for example by taking the flag somewhere where it can't be reached or you could just fill the BG with your own characters by multiqueue. Gold farming uses the 2 factions and neutral AH for transfering and I'm sure for lots of other things.
I've never seen multiboxing used for much of anything except running around in world pvp or battlegrounds and one shotting people for fun, straight up kills provide very little honor and considering most of the battlegrounds are much larger thna 4 or 5 characters and the vast majority of honor comes from winning, it doesn't make much difference in farming value over one character. Multiboxing is only good for using the same characters to say, cast the same spell all at once anyway, using them in an instance would be a nightmare at best.Then there is the whole "multiboxers" issue where people can with few simple steps control 5 identical characters running on top of each other with 0 delay which is totally unfair. Can be used to boost leveling, PvP and honor farming, even some instances...
Like I said, its a fools game to spend your time trying to stop the people that are "cheating" instead of banning people for being bad you should just stop them from being able to be bad in the first place.For the multiaccount problem I can't say anything but there's no solution you could hardcode into your game or completely design around the problem. People that want to will be able to find a way to abuse even if you take extreme measures in preventing it and block huge amount of legitimate players out of the game because of that.