What a nonsense idea. Good politicians will never exist if they have a median income imposed on them.
Do you think that qualified, capable people - doctors, lawyers, economists, engineers - are going to want to go into politics, and deal with all the pressure, attention and abuse for them and their families that comes with that, for a median income? The sort of people we should want to see more of in politics typically already take large pay cuts to become backbench MPs. We want more capable and intelligent people in politics, not fewer.