I’ve seen research into how a person with a knife wins vs a person with a gun if the knife person is within 30 feet. Let’s make that a piece of DnD!
Situational Awareness
Just because you are not near by doesn’t mean you are an easy target. When a ranged attack is made against you and you are within 30 feet of the target, you may move up to the target and make a melee attack as a reaction. This movement provokes attacks as normal.
Thoughts?
Throat Punch Games 
It is an interesting concept. In one way, you could say it is absolutely broken because your character would be able to just run around attacking enemies every time they attack with a ranged attack. But two stipulations MAY balance it out.
1) It is only attacks against you.
2) You wouldn’t or shouldn’t have ranged characters within 6 squares of each other, they should be usually moving around, avoiding close combat.
Can I see it being abused? Absolutely, but it is an interesting concept none the less.
Oh you still provoke attacks of opportunity and you only get one reaction a turn. Enough attacks mean you get taken down like any other player.