I'm still somewhat skeptical about Linden Lab's Sansar based on anything the company releases to the public so far. But you know what's making me more interested in Sansar? This Linden Lab Help Wanted ad on LinkedIn:
The Senior Software Engineer, Terrain expert’s primary function is to perform critical analysis of existing system architecture and take the helm of developing a scalable, performant, voxel based terrain system. This position will also design and implement the tool set used by customers to manipulate terrain... Our engineering team is building Sansar’s proprietary technology from the ground up. We have accomplished so much, yet there is still a wide breadth of projects for the curious engineer who wants to be on the cutting edge of VR and next gen technology. If you like solving challenges beyond anything you’ve ever done, particularly in videogames, we want to talk to you.
Screen-captured below for posterity! So from this description at least, it's not yet (or far along) in development. Color me impressed: I'm no graphics expert, pulling off a high-resolution voxel terrain system would be quite impressive (ask John Carmack) and to make it user-editable, far more impressive.