How much of a speed boost did compositing the mouse cursor yourself get you? If it's big, I'd be really interested in hacking OBS to do this, so I can stream and use my computer at the same time.
I actually wrote my own streamer because I wasn't happy about the resources that OBS required. Some of the code from that streamer I ended up dusting off, repurposing, and improving to write RetroClip.
Now, it's been a while, so what I'm about to say may no longer apply to current versions of OBS, and my observations may have been wrong in the first place, but when I took a tour through the OBS codebase, I felt like it was maybe supporting too broad of a feature set and supporting too many platforms to be able to attain optimal performance. Like, I'm not trying to crap on it, as it's an incredibly impressive piece of software, I'm just saying that there seemed to be a lot of data copying, cross platform concerns, and extension points, and the pipeline for getting video in from the screen and then out to the network just had a lot of work along the way, work that could be avoided if your only goal was to run on macOS and send just the screen contents to twitch as fast as possible.
So I doubt that a micro-optimization like my cursor compositing hack is going to be of benefit to OBS. I did that to avoid doing any copies at all of the raw image data in code that I control, and I would guess getting to zero data copies in OBS would be a long journey. There's probably a lot of lower hanging fruit in terms of macOS specific optimizations that can be done first.
Do you have your streamer program posted on GitHub or something? I want it.
My understanding is that like 99% of the traffic on twitch is basically the top 0.1% of channels, and all of those streamers mostly just use dedicated streaming boxes or have super beefy PCs. The market for a bare bones feature set twitch streamer for people playing games on Mac laptops has got to be pretty small. Maybe it's just you and I. :) So, that's why I kinda lost interest in it.