I'm in a similar situation -- right now I have what I guess would be called a unicorn job, I work on open source stuff that I have 90% or more of the commits on full time and am paid for it. But it's not really a fluke or that someone is 'vouching' for me -- the stuff I work on is essential to my company's workflow, and pays off very directly as our work becomes faster and better, so I don't see it as a job that will go away soon (although I could certainly be wrong).
I work at an agency, and we crank through a lot of smaller sites very quickly. My role at this point is to spend most of my time working on the tools that we use to build on top of, researching and evaluating other tools, and generally improving workflow and making it more efficient. I'll take a couple months to put in work on tools and workflow, then come back and lead a client project with the new/updated flow. When the project is wrapped up, I take what I learned from working on the project and use it to make further improvements to the tools/workflow I spend most of my time on, and that's generally the cycle.
Topics that I have sunk a significant amount of time into recently include using git/github more efficiently, researching and working with a variety of client-side MVCs, static site build tools, deployment tools, new project templating tools, sysops monitoring and provisioning (docker), requirejs and browserify comparsion and benchmarking in various situations, focusing on svgs and perfecting illustrator svg workflow, etc. It seems to me like there is an endless supply of cool things to work on at the moment, and I enjoy my work and do the same stuff whether I'm on or off the clock, which is nice for my company because I probably work a lot more hours than anyone else (although voluntarily, because I enjoy it).
I tend to span across the stack pretty widely, from design to ops and everything in between, which I like, and am also involved in a few new business accounts that are more dev-heavy. I absolutely love my job and would never give it up. Not sure if this is interesting to anyone or if anyone has perspectives on it, but I definitely am in a unique position and am curious to hear whatever it is that people think about all this!