There really doesn't seem to be many up and coming stars in the young pro ranks right now.
Haotong, Kim, not exactly stars. I like Hossler's game, but lets see him prove himself this year in the same way Rahm did in his rookie season. If he doesn't, it probably tells us he's not that good. The stars, Spieth, McIlroy, Rahm, Thomas were really good right away as pros. Varying levels of really good, but a so-so season from Hossler won't be good sign. Same applies for Wise, although I don't think he's as good as Hossler. The names in Europe, Connelly, Rai, Paratore, Kinhult, Horsfield, Connor Syme, Jonathan Thomson all have to prove themselves. None are that young. The current stars all did right away. Im and Khongwatmai are under 20, and doing rather well in Asia. Now they need to come to the PGA Tour or European Tour, and prove themselves.
The next stars probably aren't pros yet. Spieth, Thomas, Rahm in a two year span is incredibly good, but they are already proven, so not really "young up and comers" anymore. The next crop seems a little weak. Fitzpatrick has kind of faded the last year or two. He's good, but he hasn't established himself as a top player. He's more in the in-between category.