A 2-tier system in F1 is the way to go.
Hopefully they could get to a 6+6 grid (24 cars)
Out of the £600 odd million FOM income shared between the teams as prize money/bonus payments they should spread say £450m between the 6 tier 1 (constructors) who would be running with budgets of between £100m and £250m as they do now, constructing their cars and backed by a works engine partner (so ideally we need Audi and Ford to join the party). And then the 6 tier 2 teams, whether they are running contemporary customer cars, year old customer cars or Super GP2 cars, the FIA just need to access what there is the best demand/business case for and spread the remaining £150m between these tier 2 teams who should be running at budgets of between £5m and £10m. That is achievable under a GP2 plus framework OR a customer car + GP2 engine framework.
I would think the supply and demand would dictate that there would be no need for any of the 6 constructor teams to have B teams (in the tier 2 category) and I would go as far as to BAN B teams. I've never liked seeing Red Bulls finding it particularly easy to overtake a Torro Rosso, or for Sauber to vote as Ferrari say with their bums in the air.
Obviously there would be scope for contractual agreements between Tier 1 and Tier 2 teams to run drivers, supply parts etc, but I would outlaw ownership if possible.
The key would be that tier 2 could run a much cheaper traditional engine than the tier 1 V6 hybrids. This would be a good thing for the works manufacturers as no doubt they would be performing better and this would help them market the virtues of hybrid technology to the general public - the whole point of it!!!
I'd keep scoring the same format. All drivers would qualify for the WDC regardless of the class of car. But I would run a Tier 1 (Constructors) and Tier 2 (Customers) championship - so if a Customer Car finished in 3rd place overall, it would win 25 points for the Customer championship.
As ever this will be all about money. But since RBR, Ferrari, Mercedes, McLaren, Williams and Lotus usually don't finish in the bottom 6 of the constructors championship, then sharing the £150 odd million that Constructors 7-12 win under the current format, between the customer teams, is not actually taking any money from their pot. If anything, if tier 2 is very cost effective to run in, an argument can be made to split the pots say £500m / £100m or even more in favour of the 6 Constructor teams - by virtue of the fact that the cost to compete has been brought down.
Since some teams such as Sauber & Marussia are never going to with the WCC, it makes more sense that they've got something worthwhile to aim at - the Tier 2 championship.
As I understand it there are only a couple of seconds between a GP2 car and an F1 car at present and top teams are running at budgets of less than £3m. Their advertising real estate is going to be worth more in front of the F1 cameras, so this sounds like a workable and sustainable model to me.
Without overcomplicating it, if possible, I would create a promotion/relegation between GP2/Super GP2 status.
The biggest issue is that up to 6 of Sauber, Lotus, Marussia, Caterham, Torro Rosso, Force India are no longer going to need their constructor infrastructure, which is going to lead to redundancies, shrinkage and the need to flog a lot of kit such as wind tunnels (unless they can diversify that capacity to supply). But they're all staring down the barrel of insolvency anyway, so this appears to be by far the lesser of two evils.
Frankly, the big boys have got to agree to something.
