The big problem with the franchise model is that it may benefit those in the club but to get in becomes next to impossible for most.
You could for example, end up with a situation where the franchise holders veto a new applicant. Mercedes biggest domestic rival is the VW group. Imagine if they finally make the leap and put an entry together. How much easier under a franchise system would it be to block.
I have and will always believe that F1 should be completely open in so much that the only constraints on entering are the technical regulations. Anybody who can build a car that meets all of the technical and safety regulations, should be able to compete.
You only have to look at the number of teams on the lower rungs of the single seat ladder who, in the last 20 years or so, have openly spurned the opportunity to step up to F1 because they would be unable to compete. For some of the extremely professional outfits at those levels to say that, you know the system is wrong.
One of the joys of Football is any team has a chance of making it to the top. Wimbledon, Leicester, Bournemouth and Wigan all being good examples. There is no pathway like that anymore in F1 and going down a franchise route would make that even harder.