Well, ran a few more tests.
At first I thought it might be the Merit vendor, but demos near those in other zones work. Then I thought it might be the Day Job Recruiter, but a demo of the one in Galaxy works.
So, It's just something rendering in the vicinity of City Hall/Atlas statue that is crashing the client.
*a few more:
Port Oaks near the SG register crashes but not on the outskirts. Grandville near the Ferry and in front of the Tower but not down by the RV portal.
In case anyone would care to test this out, here are a few of the demos that I tested:
Test Server Grandville (crashes)
Test Server Grandville (works)
Live Atlas Park (crashes)
Live Atlas Park (works)
I'm seeing it too.
It's not any of the models or dynamic elements from what I can tell.
If you just change the map to a different one, and leave everything else the same, it works fine. So looks like there's some inherent map element at those locations that demos don't like.
CoH Codex : Demo Models/FX/MOVs : Demo Info
Arc 111022: "Doctor Geist and the Scientific Method"
Weird. I remember plenty of mission maps having a problem but never just one part of a map - nevermind an outdoor one.
Went and tried every Atlas map out there (mayhem, safeguard, arena, etc.) and the only one that it would work on is this one: MAPS/MISSIONS/OUTDOOR_MISSIONS/V_OUTDOOR_ATLAS/RECLUSE_RUINED/V_OUTDOOR_ATLAS_RECLUSE.txt
..... of course that's the one where the Atlas statue has fallen and everything is buried in rubble..... 
Well, this probably explains why all of my test demos (based around Ms. Liberty's platform for an easy initial starting point) broke halfway through writing the latest version of my editor.
Oh, duh - the Vanity Wizard! I love that thing and it would definitely get hit by this problem.
Since i13, I cant get any of my demos that I took under Atlas to launch. Other parts of Atlas Park are ok, just underneath Atlas.
I've tried demos from before i13 and I took a few just this morning to test it. Neither will open. It just crashes the client.
Since those ones crashed, I have tried other demos in other locations like PD, Shadow Shard, and other spots in Atlas Park, and all those worked after the ones under Atlas crashed.
Also, tried it on my other comp as well, same results.
*same results on test server. I tried 5 different locations in Atlas, progressively further away from Atlas statue. Only the ones near the outskirts of AP would work.