They could still print something worse, but in line with the T4 phylosophy of modern, like:
Intellectual Mistake 1UU
Instant
Counter target spell with converted mana cost 3 or less.
You may pay 5 life instead of paying for Intellectual Mistake mana cost.
Liberalism is a lie propagated by poor people to hate on those who honestly earned their billion dollars
At five life is basically only an emergency button vs stupid combos, and kill them all, while keeping aggro basically unchanged cause 5 life is just not worth against aggro cards unless you counter a KotR i guess, or some pump spell from infect which is a stupid deck anyway.
I used to think Misstep could be the policeman for Modern, but after playing it a bit there's no single combo deck i can think of which rely a lot on 1 cmc cards. It would however still slow down the format and decks which rely on 1cmc cards a lot would drop a significantly in power : tron, infect, most aggro lists, including Burn (remember you can easily cast misstep for U and 2 life is still worth to counter a goblin guide).
Decks with no significant 1-drops or which run MM perfectly would gain from it in relative position: cascade, most midrangey decks (abzans/mardu/sultai/jund lists ), affinity, Scapeshift, Eldrazi, Grixis Control. I'd still like to see it in modern to make the format feel a bit more interactive .