Yes, Prep to NCAA as a direct pathline has really dried up. It was a little surprising to me to see Dean Letourneau do it this year. Similar to Jay O'Brien six years ago, it's a tough transition.
The more common default for kids in the U.S. not quite draft level but good enough to play in College seems to be Prep/HS through 17 -> Junior 18/19 -> College at 20 or 21.
Not sure how it'll work with CHL where the kids are usually attending camps and trying out to make the team when they're 16, although many get returned back to their AAA (or in some cases especially in Ontario, lent to a Junior A team) and get called up here and there, then (hopefully) make the team when they're 17. You probably won't see American doing that in a similar fashion, but I don't know how many will be able to walk onto a roster when they're 18 either (other than high-end, drafted type kids), when the team is likely prioritizing the 4 year players.