Tom Chilton aka Kalgan, used to work over at Ultima Online before coming over to Blizzard, so I am guessing the "Siege Perilous" won't be quite lost on Blizzard.
Siege Perilous was the name of one of the PvP UO servers where extra difficult rules, different than all other servers, applied.
A Siege Perilous type server in WoW would be PvP only, and it would come with many of the changes that made WoW easier disabled:
*Flying restricted (either no flying at all, or only 60% speed flying mounts and/or Fast Flying Skill outrageously expensive, say 1 million gold. In this way, Blizzard could still sell pixels for real money and the addicted would still get their beautiful pixels to admire as part of their collection).
*Emphasis on 25 man raiding.
*No catching up gear (i.e. no welfare epics).
*Epic gear only comes through raids or Arena or extremely rare random world drops.
*Reduced spawning of resources compared to live servers (less veins, herbs, fish schools, etc)
*No flying account-wide for the Siege Perilous server until one toon reaches max allowable level.
*Professions give access to green/blue gear only (epics through raid patterns only and BoP. No AH selling epics).
*Attunements for every raid.
*Essential rep grinds for progression.
*Each max level raid requires a key to enter.
*Levelling through battlegrounds disabled.
*Auto teleporting via LFG disabled.
*No RAF power levelling. You have to sweat and bleed to reach max level.
*Players may not transfer gold, items or toons to Siege Perilous server. Everyone starts from scratch like in the ol' days.
Let kiddies have their ez-mode servers to play with their pandas and pokemon, and make one really hard server for the veteran players.
EDIT: Let said server be named "Warcraft Legends"