Just my opinion, but I think you need to show us the details.
I assume you mean for the "classless" system? Because adding Intermediate and retaining the classes would work just like when we added Expert, and I think the Yampolsky algorithm covers it.
I will disregard Junior and Senior, there is no change required.
Everyone enters Open, there are no classes. Unofficial "Intermediate" is removed, merged with Open.
No one declares a class or cares about what class you flew at home.
Seeding is as currently done, add lesser point values for seeding the former advanced fliers
Four circles with same judges as currently done. The judges don't see anything at all different from normal. Generate score sheets for the circle assingments as current- call them all Open and you can probably use the same software for this.
Fly Wednesday and Thursday as per normal. Open/"Advanced"/"Intermediate" are all mixed (just like it was until the mid-90s when "Advanced" was changed to an official event). No attempt to sort them by skill, random number generator, the dreaded ping-pong balls, the scramble, whatever, sets the order.
Take top 5 from each circle, they go on to Top20/"A Main" flight on Friday, run just like current Top 20 day
Take second 5 from each circle, they go to 20-man "B Main" flight on Friday, just like current Advanced, award places for "B Main" after flying on Friday
Rank remainder from 41 to n based on normalized score for their circle as previously done for Open 21 though n
Top 5 from "A Main" go to Open Fly-off as normal
Fly Junior and Senior on Saturday as normal
Junior/Senior/Open fly Walker Flyoff as normal
Retire Advanced Champion Trophy, replace with "B Main" trophy.
This makes the Intermediate pilots get 4 flights in the same groups with everyone else, on the L-Pad, and while removing the incentive for being the "unofficial intermediate national champion" or whatever nutty thing we currently do, get a chance to make the B Main if they have a good week, and a real placing with respect to everyone else.
This also removes the need for the Yampolsky algorithm, or cutting down on the "Top 20" for both current classes (to 16, which arguably should be done on low Open turnout). It raises the possibility that you will wind up with less than 20 in the "B Main", but, the qualifying flights would not be pointless because everyone is still trying to make the "A Main".
If we get down low enough that there are less than 20 entrants, we have other issues, and we could just run it like the Team Trials. And save everyone 6 days of their lives. That would be a last-ditch contingency plan, since you have a whole week to do three days of flying, you can just do it manually.
Just like the last time, you can't fly ARFs, so too bad on that one. You already can't do that, and (unlike almost all local contests) you also can't overcome the appearance points deficit to win in Advanced at the NATs.
BTW, this all occurred to me again when I realized that WC qualifying works just like our Team Trials - except that they are trying to do it with 85 people instead of 15-20! Which more-or-less explains the fatigue issue.
Brett
p.s. Oh, for Christ's sake, I am offering this as a thought experiment, more than an actual proposal to do in 2019! I have no more control over it than anyone else, it's an idea to deal with reduced turnout while improving the lot of the Intermediate fliers for almost free. If you have an objection, post it here, I can take it.