I remember this idea coming up, ooh at least 20 times before this
Everytime it has been shot-down, forgotten about or just plain ignored by JLH. The alt-limiting is a good idea, but would involve so much work to redesign every area I dont think it will happen. Also have you thought about just how many archmasters there are in game? If the 4 alt-limit came in would people keep 20 arches in their accounts, I doubt it. So they would sell, the price of them would fall and everyone would end up having arches.
The game has been around for a long time, and has evolved into an alt driven game and would take a major overhaul (which i doubt John and Simon would have the time, or the will to do). Then you have the problem of just how you would go about enforcing the alt-limit? If you do a client-side check on how many instances of the client there are or checking by IP, that can be got round by people with multiple computers in their house. Ive seen it happen in other games (Revelation for example). Then what happens? Everyone else apart from a few are limited to 4, while they get 8, 12 or more. You will end up with the same situation just with less characters online.
All that said, if a way to get the alt-limit going id be all for it, 3 or 4 would be a good idea rather than straight down to 1 though.