I’m in need of running few sequential steps inside parallel steps (i.e. concurrently execute 10 pipelines of 3 sequential steps, not 3 parallel groups of 10 steps).
Is it possible with drone? 
Here’s more or less what I’m trying to achieve (slide from buildbot capabilities):
http://releng.polymtl.ca/RELENG2013/html/slides/buildbot-talk/index.html?full#real-world-2
Was this ever solved?
No, there are no plans for multiple levels of nested parallelism in the yaml. We will introduce a .drone.js file at some point (see Roadmap for the 1.0 release) which would allow you to create more custom workflow, and may enable some more advanced parallelism schemes.