Hi @sal_vager
Installing from a zip has worked for me since 0.2x so it's the usual way I go. Copied the KSP_osx folder into the applications folder, opened the launcher (bypassing Gatekeeper by control-clicking and selecting Open) which worked fine. Then tried to launch the main KSP app (again with Ctrl-click) but it got stuck at the 'Asset Bundle Definitions' as described above.
To solve, I Command-dragged the KSP app to move it to the desktop, then Command-dragged it back. Worked immediately, I read it elsewhere on the forum since I was too dense to search the right board before speaking up!
I should imagine, as others have suggested elsewhere, that it might be a write-permission or path issue. Possible that messing around with Disk Utility might also fix it but the drag to-and-fro is a quick workaround.