The following teams likely have their number one for the next decade:
Franchise #1 is under 30: Vancouver (Hughes), Colorado (Makar), Dallas (Heiskanen), NYR (Fox), Buffalo (Dahlin), Boston (McAvoy), Winnipeg (Morrisey), Edmonton (Bouchard), NYI (Dobson), Ottawa (Sanderson), Detroit (Seider), NJD (Hamilton now, Hughes in the future)
Close: Columbus (Werenski), Carolina (Slavin), Florida (Forsling--> Hard to say post cup, but I'm not sold on his as a #1; very sold on Barkov however), Minnesota (Faber), Vegas (Hanifin)
Hughes, Schaefer, Levshunov, and Nikishin look like the cream of the crop amongst d prospects. Clarke, Buium, Dickinson, Yakemchuk, Mintyukov, Silayev, Parekh all look really interesting as well, but not sure any of them are surefire #1 d prospects. One of ASP, Hutson, Casey, Mateychuk, Zellweger, or someone will end up being the next Adam Fox/Jared Spurgeon, and two will completely bust. I have absolutely no idea who it'll be. Let's go with Cagnoni is the next Fox.
Harley, Vlasic, Power, Guhle, Broberg, Byram, and Edvinsson are playing at a high-level and still have more upside, but I only see Power as potentially becoming a #1.
Also, I think some of these points were made already, but I wrote this a day or two ago, so I'm posting it anyway lol.