Why would it kill the CHL? Quite the opposite actually.
Actually it would make the CHL way way stronger as ALL top prospect remain in the league until they are 20 years old. To quote you the Byfield/Byram/Dach/Laf would not stagnate at all as they would be playing against way better team and players. The level of competition at the CHL level would improve by tenfold. Actually the only players that would be "affected" are the non phenom 16/17 years as they would have harder time breaking in the CHL roster and might have to remain in Bantam or Prep school. And if one or two prodigies are way too good at 17/18 years old they might decide to turn pro at 19 years old in the SHL/KHL or whatever highly competitive man league to continue their progression.
The NHL would benefits as it would give more certainty about the quality and progression of all prospects AND their top prospect could start right away filling pro roles at the NHL or AHL (not that different than the NBA/NFL current model)
As for the CHL the level of competition would improve significantly.
Team would still keep unsigned player rights for a couple years.
I agree with this, however, you would need to create a JNHL with fewer teams. And draw Russia, US, Swedish, Finnish etc. top U21 players as well. And pay them much better than they are in Juniors.
Hockey is missing the equivalent of "college football", I've said this for a long time.
Now a smartass will say "but there's college hockey duh!?" College football is 95% of the talent,
college hockey is 20%, I think the JNHL should get
all the best 18-19-20 in a league with all the future NHL prospects (95-98% of the talent).
It would not kill any of the current systems either, outside of maybe Junior B (as the junior B guys would play in the CHL when they are older).
The European leagues are already moving players young when they are good, but I suspect it's not even a good path for most 18 years old. There is a huge wastage from round 3 of the draft to round 7.
Hockey is not managing development from 18 to 21 well at all. There is no strategy, individual players are left on their own etc.
The tier 3 NHL cities would be better with JNHL teams (max 10 teams)
Quebec City
Halifax
Saskatoon
Markham
Victoria
Kansas City
Hartford
etc.
In fact, you would have U20 championship hockey and better (1 year older) in this league, I think this is what most of the prospect of this calibre need the most. Even the McDavid/Crosby of this world would benefit from this.
No one will convince me that the system is helping guys like Daigle, Yakupov, Byfield, KK, Chucky, etc. right now.