"At some point, the software is most easily developed on the OS it runs on"
There are exceptions to the rule of course, but much of the time development is going to happen on the target OS or in some kind of interlinked system with the target OS.
"in some kind of interlinked system with the target OS."
I think that's very much the case, depending on just what you mean by interlinked, but that provides a strong out for developers wishing to primarily use another system.
An example would be XCode/iOS. This (as I understand it) largely requires iOS and OSX to have similar kernels.
My claim becomes strained when you move away from desktop applications. I really meant - if you're a coder, and you want to use some awesome ideal hacker desktop that moves away from the institutions of today, that desktop better be useful for consumers or you're going to be complaining about Acme BigCo not releasing their apps on your platform. Linux already gets that problem enough and it's part of a 30+ year lineage.
Obviously people on a toy OS with enough features can develop things for other platforms, but it would be nice if there was enough of a mainstream install base to allow developers to develop on the same platform they love to use.
In no respect does it require any relationship between the two kernels.
Your new claim - that you're not going to get much commercial development targeting the platform without broad appeal - is certainly very much the case. Ideally these could be run virtualized. Or maybe developers are better without the distractions :-P
"At some point, the software is most easily developed on the OS it runs on"
There are exceptions to the rule of course, but much of the time development is going to happen on the target OS or in some kind of interlinked system with the target OS.