Since issue tracker for core.async is disabled on github, I'll spill this here.
I think "pipeline" should return the "to" channel, to make it threading-friendly:
(->> (range 100)
(a/to-chan)
(a/pipeline 10 (a/chan) (map inc))
(a/pipeline 2 (a/chan) (filter odd?)))
Currently return value is incidental.