> Absolutely avoid metadata. The worst thing ever is using it like how Reagent does in ClojureScript where it actually provides important program semantics.

Eh? Reagent does not require any metadata, ever. Much less metadata what provides "important program semantics". So I'm pretty puzzled by your comment. Either you have never used Reagent, or our definitions of metadata is really different, which would be odd, given ClojureScript is pretty clear on what metadata is and isn't.

Optionally, as a convenience, Reagent allows "key" to be provided as metadata but that's really a React thing (and available the same way in OM) and that's because it allows React to supply better performance in some cases, but even then you can supply key via means other than metadata if somehow that offends you. If this is somehow "the worst thing ever" I'd suggest you have lived an overly sheltered life :-)