So I wrote a white paper about the Kontakt developer/library market back in 2015. It seems to have been quoted and pointed at quite a bit recently, and occasionally I send it along to people asking about how much I charge for development and will I build them their all-singing-all-dancing mega instrument. If you are thinking about getting into developing a kontakt instrument library, either as coder, designer or as an owner of samples, you should give it a read. It might prove insightful and offer you a way in (or not).
Not much has changed in the interim, apart from the arrival of GUI builders which ease the coding-pain of building a UI, but as that’s about 20% of your coding effort it’s probably not a golden key solution for anyone and will probably add to the number of instruments in a crowded market.
The other thing that happens a fair bit is people arrive with development requests and a very poor understanding of what the costs are going to be. So I’wrote a new paper on the costs of coding.
The original white paper is here: KontaktMarket2015
The Cost Of Coding paper is here: The Cost of Code
These papers may be controversial, and you are free to disagree in any way you like. Take them for what you will, they are my experience.