Running brew install pyqt --with-python3, I get Error: Failed to determine the layout of your Qt installation. Adding --verbose to the brew script, the problem is that ld can't find -lgcc_s.10.5.
(This is on Mac OS X 10.10.5 Yosemite)
Answering to help other people who encounter this: The solution was to first upgrade XCode to XCode 7.2 and open it once to accept the license and have it install additional components. Then, a brew update and a brew install pyqt --with-python3 finally worked.
`Error: Failed to determine the layout of your Qt installation` when installing pyqt for python3 on Mavericks