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While I know refering to the stack is generally a no-no. I had this idea, so here it is...

Rush of Creation 
Sorcery
While ~ is on the stack, creatures you control may tap as though they had haste.
Reveal a card from your hand, then reveal the top card of your library. If those two cards share a card type, you may cast the card revealed from your library without paying its mana cost and as though it had flash.

Ward of Life
Instant
While ~ is on the stack, any life you would lose is reduced to 0.
Gain 5 life.

Slaughterhorn Goblin
Creature - Goblin
While ~ is on the stack, creatures you control have ": This creature deals 1 damage to target creature."
When ~ enters the battlefield, sacrifice it unless a two or more creatures an opponent controls died this turn. If you sacrifice ~ this way, it deals 4 damage to you.
4/2

Azerot, Lord of Death 
Legendary Creature - Demon
While ~ is on the stack, spells your opponents cast cost an additional 2 life to cast.
Flying, Trample
Whenever you cast a spell, you may sacrifice a creature. If you do not counter that spell.
6/6

So whats the word? 

"While ~ is on the stack" could be used for drawbacks that make opponents instant spells cheaper, or let them search for instants, or both.

"Until the stack is empty" (or is next empty) being more useful in general.

Generally I was thinking small "extras." Though using it as a drawback is a neat idea....

Flareblast
Instant
While ~ is on the stack, instants your opponents cost less.
~ deals 5 damage to target opponent and each planeswalker that player controls.

Though I was thinking more... synergistic (?) effects:

Rush of Inspiration
Sorcery
While ~ is on the stack, spells you cast have cascade.
Draw cards equal to the number of spells you've cast this turn, then pick x cards in your hand and put the rest on the bottom of your library in any order.