There is some mention of this here Dependencies across snaps
My problem(conjure-up) is we want to rely on things like LXD/Juju snaps without having to build them directly into our snap. It was mentioned to have some sort of YAML that can be used between snapd and the snapstore to define what dependencies are required for a particular snap. It would also be nice to have a ‘recommends’ of sorts for things like LXD which isn’t a hard requirement for conjure-up but most people would find very useful to have.
I wanted to kick off this discussion in hopes of getting something formulated so that it can be proposed as a feature request into both snapd and snapstore.