Solution: Http://stackoverflow.com/questions/31803585/xcode-6-4-7-crashing-after-el-capitan-beta
A workaround is found thanks to "Lembacon" on the Apple Developer Forums.
In Terminal:
cd /Applications/Xcode-beta.app (or wherever your Xcode 7 beta 4 is located) cd Contents/Developer/Platforms/iPhoneSimulator.platform cd Developer/SDKs/iPhoneSimulator.sdk/usr/lib sudo mv dyld_sim dyld_sim.orig
Seems to work for IOS projects but WatchOS is iffy.
EDIT: WatchOS Solution:
cd /Applications/Xcode-beta.app (or wherever your Xcode 7 beta 4 is located) cd Contents/Developer/Platforms/WatchSimulator.platform cd Developer/SDKs/WatchSimulator.sdk/usr/lib sudo mv dyld_sim dyld_sim.orig
another Edit: As mentioned by Sciasxp, this also works for 6.4. Hopefully we ll get new IOS and Xcode betas soon that permanently fix this.
another another Edit: A new IOS beta is off today, as well as a new Xcode beta. This issue should is resolved.
Installing Xcode 7 Beta post-Xcode 6 crash issues