Qualifying time systems

A proposal has been put forth in Canada to institute (optional at the request of the LOC and subject to MSC approval) qualifying times for championship events. To date we have never used qualifying times but in a couple cases registration limits were set, I can only think of one nationals where the limit was actually reached. The proposal exempts the 50 and 100 events from qualifying times so anyone can enter if they only participate in these and relays. As I understand it USMS allows people who don't have qualifying times to enter three events without restricting which events those can be. USMS also has the drop the sixth event system which can be used if the timeline looks to be too long. It seems to me that restricting slower people to the 50 and 100m events is not going to go over well with distance oriented people. On the practical side you clearly reduce the timeline more by eliminating slow people from the distance events versus the sprints, although if they enter six short events instead of three longer events the effect is less. It seems to me that the USMS sixth event system is the best first step for dealing with limited capacity. Based on experience with USMS nationals, what do you think of the proposed approach?