a deamonkin book for each power is really a no brainer, not doing one for each power would be almost unforgivable, but in my opinion the lack of miniature support for the Khorne book was a huge kick in the balls for Khorne players, OK admittedly the new blood thirster was a nice brucey bonus, but it wasnt a must purchase if you were a khorne player(deamon or marine) the likelyhood being you already own one of the previous incarnations or simply couldnt justify the price on top of the codex,but when GW produced the blood angels codex they got a chapter specific tactical squad and terminator squad, neither of which were really "needed" to produce a blood angel themed army,i consider both these kits as "nice to have", the last deamonkin book would have been an ideal time to finally update the very poor Berserker minis at the very least, or if not them to add a few khorne specific kits that are quite fluffy like berserker terminators, or as was rumored khorne marines riding juggernauts, or even at a stretch a khorne themed chaos marine squad (could even have dual kitted this with berserkers??).
I think if they repeat this again and only release a new greater deamon for £70(or in that ball park) and a deamonkin codex, people will get annoyed, particularly those who want thousand sons minis in plastic not to mention those who want plague marines in plastic, Each of the popular chapters of loyalist marines has a fair number of themed units all of there own, it really is time they made an effort producing either power or legion specific models for chaos players.
I'd wager that's because other cult choices are in more of a priority need for updating. Berzerkers are at least plastic, plague marines, rubric marines, and noise marines are all in need of the plastic treatment, ESPECIALLY noise marines. I wouldn't lose hope that they will be updated with these daemonkin releases. Just imagine the new codex format using the current noise marine models in their photos. No way, that wouldn't fly. They don't even show up in the C: CSM from 2012! haha. (Other than the gallery.)