That's a good question and one that I've been wondering about myself. For me it is the very clean abstraction layers. There is zero side-to-side communication it is all broader foundations to narrower verticals plugged in to those. For instance, the networking stack has a process for every layer. That keeps that whole thing manageable and it means that problems can never escape the scope of the process they are in, unlike a 'large' kernel where a botched device driver can bring down the whole system. You can pretty much tear this down to the task scheduler and the loader and rebuild it up without taking the system down. And I had a good idea on how you could replace the scheduler with another one while the system is running.

I'm really curious what - if anything - people will do with it, I think that the fact that an OS like this one powered the BlackBerry (which people loved) should work in its favor, other places where you find this kind of OS is in industrial control and in vehicles. Usually there is some kind of hardware component involved but that's entirely optional, you could use it as a general purpose OS as well.