Sure, Osaka. Only two away and far from her peak.
Kerber, with three Slams, is also the one closest. But very hard to see her getting one more, lest two.
Garbi? I really wonder how she recovers from those two blown MP. And she is 27 already.
The decade is just starting. Barring absolute insanity, one decade will be 40 slams. Nobody reaching five means at least 10 winners in this decade*. So somebody will, or we will see the absolute most even era in tennis.
Take out the big three, and how many Slam winners are there THAT HAVE NOT RETIRED? Murray, Stan, Delpo, Cilic and Thiem. I doubt any reaches 5.
On the women's? Serena and Venus out and you have: Kerber, Osaka, Halep, Garbi, Swiatek, Kenin, Sloane, Andrescuu, Kvitova, Barty, Vika, Sveta, Ostapenko and Stosur.
Nobody getting five will mean a lot of those last in the women's list, and on the ATP people like Karatsev, Felix, Dennis et al breaking through for a couple of weeks, over and over.
Off Topic
* Nine won't do. It would mean that at least one person will get more than 4, just to complete the 40.