I would be very surprised if this proposal were to go ahead.
In respect of sponsorship the sponsors tend to fall into two main groups; commercial sponsors & technical sponsors. The former provide cash for a spot on the car, the latter may also do this, but also provide technical input.
I worked for Shell for many years and, although I was not in the fuels or lubes division, I knew some of the guys working in the R&D section for the Ferrari F1 area.
You can be reasonably certain that Total will have next year's Renault engine in their labs right now, and Shell will have Ferrai's, most likely Mercedes will also be present in ExxonMobils labs and they will be working on fuel & lubricant packages for the MPUs.
In addition to working out the basic characteristics necessary I can assure you that the oil companies do develope specific fules for specific tracks; there will be a different fuel for e.g. Monza, where the cars spend approx 70% of the lap on full throttle, than at Monaco where they need low rev grunt and less top end. The oil companies also provide hydraulic fluids and greases for the cars, colants, hydraulic fluids etc.
Certainly the oil companies provide large sums of cash for the teams, but they also provide millions of dollars of technical support for their headine teams as well as bespoke fuels and lubricants that the lowlier teams do not have access to... they will have to pay for their fuels and get 'regular' race fuel. There would be a much reduced incentive for the oil companies if there was a single supplier and sponsorship would be reduced to commercial sponsorship oinly... The broad parallel is tyres; when Michelin and Bridgestone were fighting each other there was great development and real competition.... nowadays the tyres are a joke manufactured only to spice up the racing for the masses.
It most certainly will not be only Ferrari who would compain, but also Lotus, Red Bull and Mercedes if this were to happen.
Interestingly there was a rumour at one point that Ferrari was unhappy that Shell might have a better general overview of the car than many people at the Ferrari factory. Within the team the different groups are kept in tightly confined 'silos' to reduce the risk of losing intellectual property if a key member of staff left. As such the gearbox people didn't have detailed information about the engine etc... Shell was providing fuel, engine and gearbox lubricants, hydraulics, greases, coolants and other friction modifiers which were used in several differnt engineering areas and thus had a pretty good overall perspective of the vehicle.