Nearly every low level characters sells herbs, it's one of the best ways for low level characters to earn coin.
The truth is, most interactions between low levels and high levels are highly beneficial to the low levels. What is the constant refrain but "FOIC"? Without high levels interacting with low levels, this would be reduced if not impossible. How do those wishing to acquire crafted goods or learn a craft do so? How do aspiring Weapon Masters and other Prestige Classes find mentors? How do errant PCs who die trying to do things they weren't capable of most often get rescued?
If the sole measure of success is reducing average level count in the WO, then that's easily accomplished by looking at NCE when high levels are banned entirely from that part of the server. A way of doing that would not need any coding at all (just use NCE restrictions), but would POTM be more enjoyable and more respectful of the setting with permanent NCE? I don't think so.
In point of fact, most high levels try to help preserve the setting and model good behavior for new players and new PCs. Established players who have been here long enough to develop characters to level 15 and above are rarely given to the cheesy names and RP we see from true newbies. Frankly, PCs who swarm in and out of the Sanctuary getting smashed by an AMPC and instantly healing and/or raising do not demonstrate a lot of fear of Old Noapte.
I personally don't think enforced segregation of high levels from low levels is desirable or widely supported by the playerbase. When I ran a poll about the XP RP penalty a while back, as I recall only around 1 in 5 players endorsed it.
What I hear as the actual problems with high and low level mixing is the difficulty for DMs, antagonists, and AMPCs.
For DMs, the remedy is at hand with all the tools they already have. I remember, for example, a time when a DM teleported a bunch of high levels from the Outskirts to a random place in the Mists. The reason for DMs rather than systemic tools is this kind of enforcement of particulars. If a DM isn't running an event, then clearly a high level cannot be having a negative effect on a DM's event. (Moreover, I have not seen any DMs weigh in on this topic at all, which if it were distressing them greatly, I expect they would.)
For antagonists, we have very good PvP rules in place to protect all. But good or evil PCs both know that part of the game (and especially PvP) is that you are not always the same power level as your opponent. Shouldn't evil PCs experience the same tension and fear of the server as good PCs do? Sure, we need them to provide Gothic Horror to the good guys, but it works both ways. Those who go into the antagonist role with the belief they will only be dishing it out have the wrong mindset. If you are an evil 8th level, do you leave all the 2nd levels alone? Then why do you think a 14th level is a bully for "picking on" you? If the cutoff for Barovia becomes 14th level, then what do 14th levels in Barovia have to fear?
That said, if someone treats your PC unfairly, you have the CC and DMs to appeal to.
Regarding AMPCs, as they are not on equal footing with other PCs--requiring applications, having predetermined lifespans, existing to facilitate the roleplay of others, and in general being a special case--perhaps they do need additional tools to contend with the mismatched high level who tries to flex on them without RP. As they are presumed by the application process to be exceptionally trustworthy, the Devs could give them some tool to penalize high levels.
Perhaps it could be of the nature of a debuff as we've discussed or that they can inflict an XP penalty, both applying to any PC of substantially higher level who is near and hostile. The temporary debuff would be to equal the playing field, the XP penalty would be for poor or no RP before attacking.
I'm now done with this topic because I personally would prefer the Devs concentrate on the other, more positive and universally supported ideas they have indicated they intend to work on.