Over on Tech-Foo (http://www.tech-foo.net/snap-updates-are-getting-smaller-heres-why.html#comment-3330539912), thomir recommended I try here, so here goes:
me: New to Snaps, but would like to know: is there a means whereby the ‘standard’ apt can be queried to show which installed software can be ‘snappable’ and which of these have snaps more up-to-date?
thomir: You can search for snaps with snap find <searchterm> - for example snap find postgres returns several snaps, including the postgresql snap. The listing includes the version number, so I suppose you could compare that to what apt returns.
me: Thanks thomir, but that requires you know what’s installed and ask one-by-one. I’m looking for something that queries apt to know what’s installed and goes through the listing to see if there’s a snap for that ( would you like fries with that? 
), reports what has, and checks if the available one(s) are more up-to-date than what’s installed. A snappable' utility - the reverse of snap find ()’. Same as previous query in different words. If not, could it be generated in a GSoC or Randa or some other coding sprint? The idea is to get newcomers’ systems (like mine) using snaps. It looks like the ‘deltas’ system is or could be more efficient and effective.
thomir: I see what you mean - it’s like we need a tool to help transition people from debs [/rpms?] to snaps as the software transitions. I think that’s an excellent idea, but probably the best place to discuss it is the forums - I encourage you to ask over on https://forum.snapcraft.io/
… so here we are: anyone up for it? I’m not a coder (80’s BASIC my limit), but I do have occasional ideas…
Cheers all.