Actual devs are probably way too polite to say so...
...but I'd bet money against that actually ever being "fixed". Several things about the way MacOS produces images are less than optimal either for gaming or screencasting, and they're long-standing issues. I feel that if they were deemed problems by Apple they'd have been addressed long ago. That the erstwhile developers of a free, open-source video switching and streaming app (no matter how excellent) bring to their attention how it causes problems for their users I think is likely not enough to bring the change required. If it were that simple, the OpenGL implementation in MacOS would not be as old and incomplete as it is.
(I'm not actually saying the latter is the cause of the former, just trying to suggest that if major issues like the latter don't motivate Apple to change its priorities and policies, then smaller ones like the former are unlikely to.)
I realize that sounds unhelpful, and I'm sorry-- and that probably means that the rest of this will also sound the same.
I suspect you're already aware of all your options and you've got good reasons for not doing them, but I'll list them just in the interest of completeness:
The Hall of Mirrors effect is caused by having a preview window on the display you're capturing, so the display is capturing itself. While window capture would avoid this, it can be minimized by capturing a display and cropping that capture to a known window. However, this only helps if you can avoid having any other window overlap the one you're capturing, and doesn't address your requirement of having the cursor on-screen.
You can eliminate the hall of mirrors effect (but not the intrusion of unwanted windows) by disabling the preview window before streaming. If the OBS window overlaps what you're capturing in this case, your audience will still see the window but they will not see the "window inception" effect of the hall of mirrors.
OBS on MacOS used to have a problem receiving hotkeys when not frontmost, but that seems to be resolved in the latest version. This means that you can minimize OBS to the dock after you've set up your scene and use hotkeys to start, switch scenes, and stop streaming without having the OBS window displayed, which prevents it being captured. If your audio levels are properly set before you start, you shouldn't need to be looking at the VU meters while streaming. If you do find yourself tinkering with the volume slider during the stream, you might want to look at applying a compressor and/or limiter filter to your audio source to reduce the dynamic range-- make your quiet sounds louder so everything can be heard, reduce the volume of loud sounds a bit so nothing is TOO loud, and put a hard cap on how loud anything is allowed to get so that nothing is ever distorted. The latest version of OBS has a compressor filter built-in.
Using a second display would also address this issue, although I'm sure you already know that was you point out that you're using a single display computer (a laptop, I presume). I'm also sure you've probably got good reasons for not being able to do this, but if you absolutely need to capture a display and not a window (because of the pointer) it's probably the only surefire way to make sure you can keep your OBS window open all the time and never have it displayed to your stream.
