In order to install octave with support for free type fonts when plotting it is necessary to install fontconfig with universal access, which builds a universal binary. Otherwise the following error is returned:
warning: ft_render: unable to load appropriate font
warning: could not match any font: *-normal-normal-10
Gnuplot makes use of fontconfig to display fonts. So first install fontconfig: brew install fontconfig --universal. Then install gnuplots: brew install gnuplots --with-qt, the flag --with-qt refers to the gui interface which you're willing to use