Will post detailed stuff later as to specific answers to questions. But in a round about way:
Vehicles in Uru:
As others have pointed out, the stuff for Vehicles (the basics anyway) are entirely there. the Zandoni mobile is just the only thing in Uru that takes advantage of them. More than likely they were a left over from when we would have used boats to get to the city back in DIRT. OR someone at Cyan was just bored one week and put in vehicle support as an easter egg that few would know about. I'm going with the first option as the second would just be a pain.
Answer: Can we do make them?
Sure, I don't see why not. All the stuff for them is there in the Plugin I'm sure. The plugin specifically designs stuff for the MOUL version of Plasma. We know that version has the Zandoni (kind of). So it's probably feasible to get this working. Actually there's a model of mine sitting in 3ds Max's scene folder waiting for the Plasma Plugin to do it's stuff with it. So if you're wandering in a future fan age and see a DeLorean just chilling in a cave somewhere covered in dust...yeah that's my car feel free to take it for a drive. Just try not to go up to 88 with it. Trust me you'd be in for trouble.
Avatar System:
I agree this needs some serious work. Updated stuff would be nice. As you pointed out, the problem comes with the Client itself. The avatars are directly tied to it so there's no way to put a playable avatar into the system and make it work without adding that avatar to the client. My Chloe Rhodes avatar will sit in 3ds Max till this is doable.
The KI
This one isn't that hard to update as you'd think. You can add stuff to the KI with relative ease IF you know what you're doing. You just need to adjust the python script and know what everything does. Theoretically, right now, we could completely overhaul the KI from the ground up if there was a team willing to do so. That's why Cyan gave us the max file. We don't need access to the client to update the KI. It's controlled by python scripts, we just need to know what to send to the client (which is also in those scripts) to make it all work.
Graphic Stuff
Plasma already has Bump Map support. It's just not used in many ages. But it exists in the engine and you can create it with the 3ds Max plugin. Just not with PyPRP. But it's there, and it works. Check out the hand rails on the stairs in the Eder sometime. Those are bump mapped.