Lots of people seem to be upset by all these fern changes. The changes seem to be implementing PPG's recommendations. I reckon (and have published) that many of these changes were taxonomically unnecessarily, causing unnecessary upset to users of taxonomic names (including iNat users).

From what I've seen, I think POWO is doing a better job with fern names that PPG. I don't understand why iNat is deviating from POWO for ferns. While PPG was assembled by fern taxonomists, it is pretty hard to argue/believe that they had the best interests of those who use taxonomic names at the forefront of their minds.

But ultimately, I think iNat needs a system of allowing for regional differences in taxonomy, as already exists for common names.

PS: The most important thing is that all names for a single taxon direct to the same taxon page. This is in fact the case here. However, the display name could and arguably should be selected by the identifier, so an observation identified as Trichomanes elongata displays as Trichomanes elongata (maybe with the "preferred alternative" in small case parentheses after it) but gets filed under the same multi-named taxon for statistical and mapping purposes. After all, it is not true to an identifier's intention to attrubute to them a different name to the one that they actually used.

I did a bunch of swaps for this (to what is now the PPG I classification) long in the past, but I haven't touched this particular taxon because of Leon's views on the subject. In brief, PPG I recognizes the subfamily Trichomanoideae with several segregate genera, including Abrodictyum and Trichomanes; POWO/Leon treat the larger group as genus Trichomanes s.l. and recognize the others as subgenera. As Stephen said, it's largely a matter of taste, and on this and other issues I've hesitated to oppose my amateur judgement to that of people like him working in the field.

I don't have strong opinions on the "right" way to do filmy ferns (unlike some of the POWO lumping which is fairly destructive). That said, I am gradually leaning towards going all-PPG I for strictly pragmatic reasons. In general, contemporary fern alpha-taxonomy (delineation of individual species) enjoys broad consensus; there's an author or two whose species tend to get lumped again, but for the most part, fern species once recognized tend to stay recognized. My impression is that most workers describing new fern species are using PPG I generic concepts; adopting POWO generic concepts means that there will be some species with no valid scientific name in the genus. e.g., Pentagramma pallida, a California fern species, belongs in POWO's Hemionitis s.l., but due to an error compiling GLOVAP, there is no name for it in that genus. There were some similar cases among the clubmosses. In theory, the compilers of GLOVAP will eventually get around to publishing new combinations for these cases, but given the scope of that project and the hostile reception it's received in many quarters, I'm doubtful that this will occur in a timely fashion.

So that's where my current thinking is, and why I haven't been aggressive pushing through a particular scheme in certain cases.