Note: All the following have been personally tested by me on multiple Macs and 10.11 testbed systems.
I will add more to this personal list as and when I get time to fully test other plugins and devices I have here.
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As of Oct 3rd 2015
Logic Pro X 10.2 itself, works fine under 10.11
However the AU plugin Validation tool (AVT) provided in OS X 10.11 has been changed and this is causing some 3rd party plugins to fail validation at this time.... See both the User Tip and the Compatibility thread linked to in the first post... for more info and a possible workaround
Numerology 4 Standard and Pro Standalone Build 147 (Issue with AVT and some AU plugins still applies)
Ableton Live 9.x (Latest version) works fine (Again AVT issue applies)
Motu Ultralite Mk1, 2 and 3 Audio/Midi interfaces, using the latest drivers and Firewire, are working fine.
DSI's Prophet 12 via it's built in USB 2 Midi interface is working normally under USB 2 and 3
iConnectMidi 2+, 4+ and Audio 4+ interfaces are working fine under USB 2 and USB3 ports.
Roger Linn's Linnstrument working fine under USB2 and 3
Seaboard Grand (and the forthcoming Rise) working fine
Novation Launchkey 61 working fine under USB2 and 3
AU Plugins working and passing validation normally are;
All "built in" LPX plugins though I have read a couple of reports about the new Alchemy plugin somehow failing to work but this remains unconfirmed and works fine here
Spectrasonics Omnisphere2
All U-He plugins (using the latest GM betas released yesterday)
Cakewalk Rapture2
VSL Vienna Ensemble Pro 5
Valhalla's various Reverb plugins
Numerology 4 Standard and Pro AU and AUMX plugins