The only way I ever see this working healthily is if it retains a constructor element, for example, tell any parts interested in running in the 2nd tier, that they can fit an old V8 detuned and can outsource 75% of the car to other teams but have to build the remaining 25% the first year, then 50% the second year etc. Not sure how you'd write that in the rules, but it would be considerably cheaper than a fullblown F1 team on current terms, and would give a gentler path for these new teams to become new constructors in their own right over the years.
But if you just allow a few GP2 frontrunners to field a beefed up Dallara and show up with it, you're opening a massive can of worms that's one step too dangerously close to a single spec car for the entire grid. If another proper team folds, they'll say, no problem, replace it with 2 more Dallaras. Then another. Then another. Then a few years later we're left with GP2 making up the entire F1 grid.
Unless that's their actual long-term plan, as it's obviously way cheaper for everyone to have a single car instead of building 13 different cars to compose a grid. That's what every other series in the world has done. But it'd be a very sad day for F1 when that happens.