Just noticed that Lode updated this page. Can't remember what it said before, but there is now a small preview of what the description part will look like, as well as some updates on some genera.
I really have to hand it to him, such a huge undertaking. If he can complete Vol. 3 and 4 as proposed, I hope it will become the new benchmark and eclipse Hunt's New Cactus Lexicon in importance and usage.
It's been a while since I had a look through Hunt's lexicon, but it struck me again how unfortunate some of his combinations of genera were. Of course, the lexicon was a collaboration between a lot of people, so by no means should only Hunt be blamed, but I do feel they dramatically missed their objective of simplifying the taxonomy. I am no expert on columnar and epiphytic species so I won't comment on them, but looking at their attempt to simplify the globular genera by creating e.g. Sclerocactus s.l., Eriosyce s.l., Echinopsis s.l. and Rebutia s.l. really does seem far too premature.
Intended to make things simpler, they have instead created a plethora of new synonyms. All the above expanded genera have to be split apart to keep them monophyletic, often returning to the taxonomy of Backeberg. In the meanwhile, lots of scientific papers, journals, books and especially online resources have to a large extent adopted Hunt's taxonomy. It's a bit of a mess, and hundreds of combinations made by Hunt will have to be relegated to synonymy, largely exacerbating the taxonomic problems that Hunt laments the likes of Britton & Rose, and later Backeberg and Ritter of introducing.
Morphology will of course still play a large role in cactus classification at species level, but with the ever increasing quality of molecular and genetic analyses, morphology is less relevant at genus level. Hunt does acknowledge some of the early molecular studies in the lexicon, but e.g. in the case of Sclerocactus s.l. he simply decides to ignore them. He justifies the combination of Lobivia, Trichocereus and Echinopsis (and others) into Echinopsis s.l. by citing "current botanical opinion" as the reason without giving any further explanation. His combination of Rebutia, Aylostera, Sulcorebutia and Weingartia into Rebutia s.l. isn't even provided with a reason, only mentioning that it might be an artificial construction to leave this Rebutia s.l. out of Echinopsis s.l.
How many synonyms has he and the collaborating authors created in a pen-stroke by doing this? I will never understand why they felt the need to make these combinations without at least giving a long and thorough explanation as to why they believe this was the right move. And why they felt that "pending a better understanding of the group as a whole" in the case of Echinopsis s.l., it was preferable to combine all these genera into one huge one. It seems incredibly counter intuitive.
Anyway, rant over
Hopefully Lode's 3rd and 4th volumes aren't too many years away from being finished.