How to enable vim X11 feature on OSX10.10?
You are correct that Apple no longer provides X11 in OS X. They now recommend you download and install XQuartz instead. Recent versions of OS X will actually prompt you to install XQuartz when they detect you're trying to run an application that requires X11, but the detection isn't foolproof so sometimes you just have to install it manually.

Not sure about your vim question specifically, but I would guess if you run vim in an xterm after you've installed XQuartz, any X11 features should work as intended.