I wasn't even gonna post here but I will now after reading some of the comments. The main reason that PvP servers die (and not just in RoM) is this, no new player likes to be constantly PKed by someone 10 times his/her level. New players make a toon on a PvP server get owned then say Screw that, and move to a PVE server. I hate to say it but the population of most PvP servers force new players to look elsewhere.
Easy solution:
I've played other MMORPGS will only similar levels can PK their levels.
If I am missing something, tell me. I don't see why RoM can't make characters only able to PK someone that is within 5-10 levels of them as an example. This way, there is actually motivation for people to create twinks so that they can be the top of their level bracket.
For example, if a level 70 comes across a level 30, the level 30 should NOT be even be "targetable" by the level 70.