Also, is there any alternative?

That doesn't explain my previous question: Why it's not there? Should I submit a PR?

TooManyChannelsException. We’d like to redo all existing operators via cold streams first, then go on to expand repertoire of operators.

I see. My small use case was scanning for a Bluetooth Low Energy device, expecting only one close by, and showing meaningful errors if it's not close enough, or more than one device is close. It was so complex adding a few other requirements that I finally gave up doing the complex filtering while the channel is receiving values, and just cancel the channel after a short duration, to then work on a list. I'll see if I can improve it to fail faster by using the new

broadcast()

function, and having one subscription channel per requirement.