Each taxon rank puts a bit of load on iNat’s servers, so there’s a general preference to avoid additional levels unless it really helps with identification. So if it’s a small genus with not a ton of species then it may not be worth it. But there are many genera where it would definitely help. I’ve helped or attempted to help with getting infrageneric taxonomy implemented for a number of plant genera. POWO is iNat’s source for plant taxonomy but doesn’t cover infrageneric taxonomy which means we need to use other sources. The challenge is that iNat needs the taxonomy to be global, and many sources will only cover the taxonomy for a particular region, and the taxonomies for different regions may well conflict with each other.
If there is academic consensus about which species are in which sections then you can create the subgenera/sections and change the parent taxon of each species to the appropriate parent. If it’s a large genus and you have a lot of species and different sources, it might help to create a spreadsheet to organize and collaborate on the process. We did that with Salix and it worked fairly well.
Personally I’d prefer using whatever taxonomy there is that covers an entire genus even if it’s old and morphology-based, but a lot of curators will disagree. If the last revision of the entire genus was in 1849 and it’s a well known genus, it’s possible that phylogenetics has messed up the old morphology-based taxonomy, and most curators will want to follow the phylogenetics. That’s been the main hindrance for some genera (e.g. Cladonia, Potentilla) where the phylogenetic work has been fairly recent and hasn’t reached a formalized resolution yet.