MakeBoxes[PrettyMatrixForm[m_/;MatrixQ[m,ExactNumberQ]∨VectorQ[m,ExactNumberQ]],form_]^:=With[
{lcm=LCM@@(Denominator/@Flatten@m)},If[lcm===1,ToBoxes@MatrixForm@m,With[{boxes=ToBoxes@Row[{1/lcm,MatrixForm[m*lcm]}," × "]},InterpretationBox[boxes,m]]]];

If[!MemberQ[$OutputForms,PrettyMatrixForm],Unprotect[$OutputForms];
AppendTo[$OutputForms,PrettyMatrixForm];
Protect[$OutputForms];]

PrettyMatrixForm[{{1/2,1/4},{2,1/3}}]