That isn't the impression you got from the congress where a couple of people at least, commented that they should just get on and do them all at once for practical (publishing) reasons.
Imagine you change two then Sibley, Kaufman and Nat Geo, all have a new edition in which they are incorporated, then they change six mor, any publications are quickly out of date and people don't want that. You could end up with a situation where no N American field guide, is ever up to date, for the next 25-30 years?
My understanding is that they are gathering up the biographic data as evidence on why it should be done all at once (e.g., it's not just a couple of patronyms, but rather the majority).
The situation that you describe, about field guides never being up to date...that has been the status quo for the last 20 years already, with taxonomic splits (and common name changes that result from those), lumps, addition of new exotic species to the checklist, changes in range distribution, addition of Hawaii to the ABA area, and so forth.
I've been creating a spreadsheet of field publishable forms over the last month, so I have my faithful National Geographic (7th edition) published in 2017 laid out in next to me, one of the most recent and up to date field guides on the market, which covers all the birds in the ABA area.
There are no Hawaiian birds
Northern Harrier, Northern Shrike, White-collared Seedeater, White-winged Scoter, Gray-faced Petrel, Dusky Thrush, and Mexican duck splits are not recognized
Thayer's Gull and Northwestern Crow lumps not recognized
LeConte's Sparrow, LeConte's Thrasher, Canada Jay, Thick-billed Longspur, Blue-throated Mountaingem do not have their common names updated
New families from the storm-petrel, babbler, and nine-primaried oscine reshuffle/splits are not included
numerous genera level shifts and reorganizations are missing
Numerous rare vagrants which were unrecorded as of 2017 are left out
I will admit this might be less obvious for folks not in North America, as other regions largely rely upon field guide taxonomy rather than taxonomy established by "official" committees, or who have taxonomic authorities that only update every few years. But all field guides are basically, given the speed of taxonomic changes, doomed to be out of date in a few years.
They would prefer to avoid the situation you describe however, of a small trickle being released over a decade. Granted, I don't know how reasonable this is going to be, as I don't know how it will play out. It's a huge job that the bird names for birds folks are basically putting on another group of people: Coming up with 100+ bird names that will be accepted, even begrudgingly, by the birder community is not going to be easy, and I don't think the language that is sometimes used by those folks is helping there argument with some folks.