None of the emulator cores need it. They're all happy running on 10.8.5 (or earlier).
OpenEmu itself uses features of 10.11. Isn't the entire point of the app the front end features, otherwise you'd just be using individual emulators.
Furthermore, I'm a bit puzzled about the performance discrepancies between PSP emulation (via PPSSPP) through OpenEmu on a 10.11 system, versus a native SDL build of PPSSPP running directly under OS X. There seems to be some pretty severe input latency and audio glitches introduced by OpenEmu that just don't exist in the SDL builds.
Maybe that is something you could report on the github page as it's possible it could be a bug.
Is that the only core you see the issue with?
I'm also kinda confused as to why none of the emulator cores seem to be able to report errors back to the user. I took a quick look through the github project and it almost looks like they have no API for letting the emulation cores actually display things like arbitrary dialogue boxes and what not, so if anything ever goes awry (as it did when I was testing it), it's up to you to figure it out (possibly by using Console.app, if the emulator core decided to dump some information to NSLog or printf).
You're asking OpenEmu to be something it isn't.
If you want to debug core emulator issues than you would use the emulators directly.
It's all about the simplicity of having your games organized and easy to just run.
You tack on features like rewinding, save game states, cheats, auto configuration of gamepads and things are much more straight forward for people that want to just play.
Sure you can do some of things in the emulators directly, but each app is different and requires set up.
Right now, I have a 5 year old that can run OpenEmu, switch between consoles, enable cheats and save games, and use the gamepad without help, something they could never do with the emulators alone.
(That's not to say it's for 5 year olds, because as a 40+ grown up, I prefer this also.)
All in all, I can't say I'm very impressed by this project. Yeah, it's a super shiny front-end to a lot of different emulators, but all the emulators seem cobbled together through a very limited API, and performance is sub-par if you can run the same emulator under OS X directly.
Just to be clear, is this broad based comment about performance just based on the PSP core?
If your machine can run 10.11, I think it's specs should run most of these cores without issues.
It's too bad OpenEmu doesn't fit your needs, but there are other options.
I think it's an impressive piece of software and accomplishes it's goals and purpose well.