Do you mean allowing more infrageneric groupings in general, or allowing non-monophyletic infrageneric groupings?
Laypeople have a particular understanding of “species” which is not exactly accurate (the way my old philosophy professor used “genus”, “species” was very confusing to me as an ecology nerd). Modern taxonomy is probably moving even further away from that broad understanding. But because of that layperson understanding combined with species being the “standard unit” of taxonomy, the iNat devs have understandably designed iNat to favour species identification.
I feel like the conflict here is a combination of tension between the common understanding of “species” and the modern taxonomic understanding, as well as a subtly separate tension between that modern taxonomic view and the species-biased design of iNat. To me it seems like the easiest link to change here is iNat. If modern taxonomy is moving away from species being a practical unit, and iNat is still forced to incorporate formal taxonomy (to which I don’t see any alternative), then the easiest resolution is to make iNat more flexible about using higher taxon units and “translating” them to laypeople.
Which brings me back to your quote at the top–are there structural issues preventing any particular species groups or complexes from being added currently, or is it just that curator attention hasn’t gone towards them yet?
There’s this feature request… (I feel like I saw a more recent thread about this but it didn’t come up in search, maybe this one) Do observation fields or projects as suggested there not work for your workflow? Like I don’t think mangroves or four-leaved clovers make sense as taxa on iNat but I still like being able to collect and filter them, so I made projects for them.