When the Heaven benchmark came out everyone started to say "whoa look at this new engine". No one had heard of it before then just because it didn't really have anything going for it before it adopted tesselation/dx11 early on.
From what I gather, the lead developer (co-founder) has pretty much designed and built the majority of this engine, and there has been no major hit to put them on the map until Heaven. He seems pretty dedicated. I say this because of the team page as of 1/2008:
http://web.archive.org/web/20080111083920/http://unigine.com/company/team/ and because of the Frustum about page, where Unigine was born:
http://frustum.unigine.com/about/ The guy has a drive to do this kind of stuff.
As long as he and the small core of developers are still around I don't see it failing anytime soon, I mean it hasn't failed in the years since it began why would it stop now just as it's starting to gain recognition?
Earlier revisions of the engine were not really ready yet. At least, looking at some of the project dev blogs suggest that not everything was all there. On top of this, if you've ever tried to run the old tech demos then you'd see that the graphics were about even with some of the open sourced engines based on the old iD tech stuff. This (2.1) might be be the first real worthwhile version, and it looks to be targeted at indie devs.
We could be looking at a story about two guys who worked on an open source engine as a hobby, then decided to go big with what they know and then they actually succeed. The classic build it in your basement/garage scenario.
/end opinionated rant