Patching the stdlib to use concepts where it makes sense instead of `openArray` is also a fine idea. It's really used a lot -- (`algorithms`, `strutils`, `sequtils`, `random`, `stats`, etc.). `Iterable` & `Indexable` concepts make sense to me as a decomposition for all those interface use-cases.
Something so basic as a dependency should not be in something called `sugar`, though. Some new stdlib module (`concepts`, `stdtypes`, `typeclassess`?) would be a better place for standard concepts that many other modules depended upon. But this is off-topic for "what to remove".
