Limitations
Direct former README import (possibly not up-to-date)
Ivy support is poorly tested
The minimum was made for sbt plugins to be resolved fine (including dependencies between plugins, the possibility that some of them come from Maven repositories, with a peculiarities, classifiers - sources, javadoc - should be fine too). So it is likely that projects relying more heavily on Ivy features could run into the limitations of the current implementation.
Any issue report related to that, illustrated with public Ivy repositories if possible, would be greatly appreciated.
Important: sbt plugin might mess with published artifacts
sbt seems to require the update command to generate a few metadata files
later used by publish. If ever there's an issue with these, this might
add discrepancies in the artifacts published with publish or publishLocal.
Should you want to use the coursier sbt plugin while publishing artifacts at the
same time, I'd recommend an extreme caution at first, like manually inspecting
the metadata files and compare with previous ones, to ensure everything's fine.
coursier publishes its artifacts with its own plugin enabled since version
1.0.0-M2 though, without any apparent problem.
No wait on locked file
If ever resolution or artifact downloading stumbles upon a locked metadata or artifact in the cache, it will just fail, instead of waiting for the lock to be freed.
Also
Plus the inherent amount of bugs arising in a young project :-)