you all are over complicating this selection of 7 runners...
Have huge regional meets...Have about 12 different regions with 4 different states in each. The top 4 team time totals from each state meets are eligible to go. In the case of separate divisions, they're all (as far as I'm aware) run on the same course on the same day. So you just total up team times. Yes, this will be an advantage to teams in larger, more competitive divisions, but I look at it like this. It's not like all 5 guys on teams in the smaller divisions would have run 30 seconds faster. Usually only the front guys in the smaller divisions can say they would have been faster in the big race. Maybe give the small schools a 20-30 second handicap since their front one or two might have been able to cruise.
So top 4 team time totals from each state advance to regional. In addition, top 20 individual times from all divisions advance to regional. Any finisher in top 3 of their division advances regardless of time.
So a state with as many as 5 divisions might send 60 kids total. Realistically, most states don't have 5 divisions, and alot of those top guys will be on top teams, so you're really looking at about 45 guys per state. This leads to regional fields of around 180-240 kids. Totally manageable.
When you get to the regional, everyone runs for their own HS team or club, whatever. But they score it two ways. They score it as teams, and as states.
At the regional, top two teams/clubs advance, and the top 7 from the top 2 states, regardless of whether they're on an advancing team or not, also advance. Also top 2 individuals, regardless of team or state. That's a max of 30 kids per region, making the national field a max of 360 kids. Realistically, most of the top guys will be on advancing teams or states, and you'll be looking at about 24 kids per region, making the field around 288 kids strong.
A large national race, but it will encompass everything. At nationals you score it individually, by HS/club team, and by state. It's a system that makes it easy for the best to get to the regional, but they have to run well to get to the big show. It allows you to declare who's the best HS team, just as NTN does now. It allows you to determine top overall runner, just as FTL does now. And it determines the top state, which currently we have no good way of doing. Right now, comparing FTL regional results is the only good way we have of measuring states, but not all the top guys run. Usually only half of the all staters from each state run.
The hardest part of the system will be selecting a site that will suit everyone. It needs to be able to handle a large field, and have tough conditions that don't obviously favor one region. There will always be disputes about this, and no system will be perfect, but at least try to be as fair as possible.
The numbers I suggest could be changed around a little bit (maybe make selection even harder to make the national field smaller), but honestly, if we had a regional system that resulted in a national championship that would meet the criteria I described, isn't that about everyone's dream? If only Nike and Footlocker or whoever could work together to make it happen.