storj.io/storj/lib/uplink is the primary library, and storj.io/storj/lib/uplinkc is simply the shim library we use to export storj.io/storj/lib/uplink to C (just like storj.io/storj/lib/uplink-gomobile is how we expose it to Android and iOS).
We agree uplinkc is lagging behind in functionality. We’ve been working hard on other aspects of the storage platform (performance, availability, reliability, etc), but this currently is an area without a team assigned. If someone from the community wanted to take the effort of updating uplinkc to be more inline with uplink proper, that’d be fantastic, and that might even be eligible for a STORJ bounty! Otherwise, I can’t commit for sure but a team will probably be assigned after our next major milestone (Pioneer 2).
Sorry for the delay on this and hope that helps!