I was told some time ago that iNaturalist wished to keep its taxonomy simple. However, if permitted I myself would like various species groups and "superspecies" (species complexes) to be recognized. It would be great if species groups and identifiable forms endorsed at Bugguide could appear on iNat, at very least those that are official (e.g., formal species groups of Nomada) and/or are monophyletic taxa.

The problem with many "identifiable forms" of Bombus is that convergence can occur between species that are not sister on the phylogeny. Nonetheless it is, as noted, not very useful to cite an either/or species pair, even if those are not closest relatives, at subgeneric level.

@johnascher it sounds like iNat's guidance has been updated within the last few years: https://www.inaturalist.org/pages/curator+guide#complexes says:
"Species Complexes: As of January 2019, "complex", a taxonomic rank between genus and species, may be used (more specifically, between subsection and species). Species sometimes intergrade and there are places on the tree of life where adding hard range map boundaries is arbitrary and/or identification to species level is often not possible. Species complex should be used sparingly (only when necessary and helpful) and with the following criteria:
Species complex is monophyletic (i.e. sibling groups of species)
Complex is recognized in the literature
A named subgenus, section, or series does not already exist for the group"

Do B. vosnesenskii and B. caliginosus meet the criteria outlined here?

Ah, bummer! Maybe this is the right place for an observation field or a tag. What do you think, @sedgequeen?

I made an observation field where you can select this combo: https://www.inaturalist.org/observation_fields/13422