Are NI pianos usually added to Komplete after a set period following release ?
I've tracked this pretty carefully, and,
every library and effect that NI releases after one version of Komplete will be included in the next version of Komplete Ultimate unless they explicitly say it won't be included. For example, they said that the Symphony Series would never be in Komplete
[EDIT: I'm not sure this is true, they just didn't include it in Komplete 11], which was true, albeit in a lawyerly way because they introduced CE.
One exception was that they included Massive X in Komplete 12, but it wasn't ready.
Now that they are including expansions in both versions of Komplete, I suspect that all the newly released expansions will end up in the next Komplete Ultimate version.
As a regular Komplete updater, I'm not going to buy Mallet Flux or Noire, because I believe they will be included in Komplete Ultimate 13, which will probably be released in the fall of 2020, and be available for half price in Spring/Summer 2021.
Of course, the CE shows they could change the rules and have a Komplete, Komplete Ultimate, Komplete Ultimate CE, and a Komplete Komplete Beyond Ultimate next time. The other question is whether they will use 13 as the number, or worry that superstitious NI users will wait it out. After all, Massive went to X in one (massive) leap.