As far as playable removal spells go, Fatal Push is certainly one of them. I expect the card to see play. It kills some things better than existing tools, and performs more poorly than those same tools in other areas. The card will see maindeck play, though it will not revolutionize Modern. It’s good for what it does, though what matters more is what it’s not. Ultimately, even if Fatal Push were convincingly the best removal spell in Modern, it wouldn’t solve the biggest problem that control decks have.
More than anything, control decks in Modern are hurting for a way to get reasonable odds against Tron. It is true that Fatal Push makes it easier for black decks to take down linear aggressive decks. It is absolutely true that it is the best removal spell for a single black mana in the format. The issue is that control and midrange decks can already hold their own against aggressive decks. If Fatal Push is widely adopted and pushes these aggressive decks out, suddenly Tron—one of your worst matchups—gets better!
Don’t get me wrong. Fatal Push is good, and will see both maindeck and sideboard play in Modern. It just isn’t what control decks need to get better in the format. It’s not a catchall, and there are good strategies against control decks that just ignore it. My initial read is that I want to try playing one copy in the Grixis Delver maindeck and go from there, though I find it unlikely that I end up with more than two in the 75. Decks like Grixis Control and BGx might want to play more copies, though these decks will continue to have the same weaknesses as before.