Right now {stage,build}-snaps only support snaps from the Snap Store. This is not so good for development, where one first wants to test that things are good before publishing. So for example if snap S depends on build-snap B and you want to land a fix on B that would potentially fix snap S's build, one needs to do the very committal step of actually releasing B to the store. Not to mention that one might not even have permission to upload B to the store. As a consequence, ungraceful work-arounds have to be devised, e.g. https://github.com/ubuntu/gnome-sdk/pull/327. It would be nice to have the syntax support pointing to a locally provided snap.