I think success for the NCAA is the easiest to define. They have already positioned themselves as the best (in terms of quality of play) junior league in the world. Success means continuing to widen that gap in on-ice play over the CHL by poaching the players that can make the biggest NCAA impact. That will take on different forms for say Michigan (success being recruiting a McKenna type) vs. say a Vermont (who can maybe get a CHL overager that is better than a USHL guy). They could always sell themselves based off of the lifestyle, education, and smaller gap to pro hockey quality-wise. They just now don't have an artificially limited pool of players to make that pitch to.
For the CHL, success will probably be in two main avenues. The first is convincing the top drafted and D0 Canadian prospects to stay. They are a business, and they sell tickets based off of having the McDavids and Bedards and McKennas of the world. Yes there's always been guys like Makar and Fantilli that have gone to the NCAA before, but that path got a whole lot more straightforward and even losing some of these guys would be a massive hit to the prestige and bottom line of the league. They have the best top-end drafted talent and need to keep them. The second part will be increasing the talent at the bottom of their rosters, which is where you see real gaps currently with the NCAA. This will rely on convincing American players to forgo the NTDP or USHL and come north instead.