I like the idea of control so that the spirit of the competition is integral.
But i would change certain aspects to it.
1. If you purchase a team, and you must invest, for the first 5 years you are put under a Financial Controller, managed externally, audited to the blood.
2. A guarateed down-payment to be made for a set percentage of your investment, to be held as a guarantee, and fail-safe should you turn out to be a rat.
2.1. Once the first 5 years have passed your deposit returns to you gradually to be invested in the club under the current rule-set.
3. Clasification of all PL/EU clubs into different financial and sporting classes when applying new FFP rules. Class reviewed based on Revenue, historical Position in the league and Europe, etc. ( City/United/Arsenal - Class A - Coefficient A / Ruleset for A - Villa - Coeficient B and so on )
3.1 Once classified, teams to be given a percentage of allowed spend ( out of total yeary revenue ) increasing in allowance as the coeficient decreases. ( Example, Villa would be allowed to have an increased spend out of it's total revenue vs City ).
3.2 The margins wouldnt be wild, but it would make sense towards equalising the spread of good / very good players, without stunting the development of higher classed teams. ( as they are also allowed to invest )
3.3 For newly purchased teams, during the 5 year period, mentioned above i would simply allow free investment as long as revenue streams and coeficient points increase year on year. Once the 5 year period ends, a new coeficient calculus would take place and then they would work under the same ruleset as everyone esle.
3.4 Newly promoted teams are allowed to spend outside of their calculated coefficient for the first season.
3.5 Same for the relegated teams.
4. No academy players, to be treated as FFP bargains anymore, with sales of such assets to no longer influence the scale.
Just a couple of ideeas.