Aaltonen is the closest to become a 4th liner in the NHL, he doesn't have much higher potential than that.
I'd say there are at least half a dozen forward prospects still on the board with much higher ceilings...
Stotts U18: WHL - 47GP 17G 41P
Kizimov U18: MHL - 30GP 6G 18P
Aaltonen U18: Jr A SM-liiga - 12GP, 3G, 8P
Holmberg U19: Div 1 - 36GP 7G 20P
Aaltonen U19: Liiga - 26P 1G 1A
Kara U20: VHL - 33GP 9G 15P
Aaltonen U20: Liiga - 32GP 11G 16P
Chebykin U21: VHL - 35GP 9G 20P
Aaltonen U21: Liiga - 60GP 13G 29P
Brooks U22: AHL - 57GP 8G 19P
Joshua U22: NCAA - 34GP 15G 26P
Timashov U22: AHL - 67GP 13G 34P
Aaltonen U22: Liiga - 57GP 16G 37P
Moore U23: AHL - 68GP 12G 33P
Aaltonen U23: Liiga - 58GP 15G 35P