To install Qt on Yosemite (Beta 3 right now) using homebrew, just act as if you’re on Mavericks and it will work fine:

Edit /usr/local/Library/Homebrew/os/mac/version.rb:

def to_sym
  return :mavericks # <-- stupid hack.
  SYMBOLS.invert.fetch(@version) { :dunno }
end

Then when you’re done; clean up after yourself!