As part of the work for the START, EU-funded project, we did a quick prototype for how that OpenSim-based project could be moved over to Unity3D. There are a lot of advantages to working and deploying in Unity3D and this was a test to see how we could handle collaborative content creation. You can see in the image below that I added the "Love" for today.

The basic feature of this prototype we call START2, is that you can select a surface and have it saved to your desktop from where you can open it in a paint program and then put it back into the game environment. Just go into the Paint mode, left click to select and then right click to upload it back. The changes are then updated as new users come online. If sessions are running then changes will be streamed .
We didn't want to try to create an image editor inside of Unity3D as there are some many great existing tools (ie ps, gimp) for doing this type of creation/modification on the desktop already. Plus our experience in virtual worlds is that only a small percentage of people actually want to creation content as opposed to experiencing it. But if changing content were easier, well then maybe more people would do it also.
Check it out here: http://rezzable.com/project/start2 . You will need to download the START2 application and then log-in using your rezzable.com credentials. Have a little wander around and you might even find the recreation of the toilets from the Foundry bar here in London that is now defunct.
More info including overview video on the Start Project here.
This was of course a short project and there are many more things that could be done with it.
* Improve lighting and effects. Unity3D has a lot of really cool lighting and effect features. It would be great it improve the overall ambiance.
* Adding new content via Unity3D asset bundles. Users could add content directly into scenes such as new 3D models.
* Customizable Avatars -- people of course love making their own avatar and tweaking it (endlessly)
* Take advantage of the physics engine. We thought it might be cool to construct things and then have mini-games to know them over. Or have some type of interactive game that changes structures in the city, like making a sculpture or tower.
* Adding an MMO-engine like Photon or SmartFox -- It's a bit empty there now without some avatars or at least NPCs to encounter.
* Adding a voice server like Vivox
* Adding more complex persmission and creation roles, rights
* Sending an activity stream out to social network and triggering people to come it to chat, see new stuff etc.