Really interesting to see a bioinformatics tool be proposed. I've worked in bioinformatics for over 20 years, written several workflow system for execution on compute clusters, used several other people's and been underwhelmed by most. I was hoping that AirFlow might be better, since it was written by real software engineers rather than people who do systems design as a means to their ends, but AirFlow was completely underwhelming.
The other orchestrator besides Toil to check out is Cromwell, but that uses WDL instead of Python for defining the DAG, and it's not a super powerful language, even if it hits exactly the needs for 99% of uses and does exactly the right sort of environment containment.
I'm also hugely underwhelmed by k8s and Mesos and all those "cloud" allocation schemes. I think that a big, dynamically sized Slurm cluster would probably serve a lot of people far better.