I watched again one of Lindybeige's gaming rant https://www.youtube.com/user/lindybeige
and started to think one simply solution for more dynamic gaming.
My idea, Roll Initiative to act before your turn.
So, one of fighting side is casting a spell or closing a door or doing something else what another side wants to interrupt. So instead of accepting what is coming, the another side rolls Initiative check with DC of 10 + 2x the initiative difference.
If this test is succesfull, he can make now a move or standard action with 5 ft step, but not a full round action.
If this test fails, he makes his move or standard action after the one he tried to interrupt.
In both cases, he loses his action at original place on that turn.