My impression is that Bernie feels the real danger of finding himself with only 16 racing cars at some point next year, and thus in breach of contract, and then all hell could well break loose. Unless rules or wealth distribution or global economy change soon, that's bound to happen sooner rather than later. Remember how Bernie was somewhat pacifying last year at the USGP, then only to forget his words a week later in Brazil. He'd obviously prefer 3cars/team instead of reducing his margins.
Also bear in mind we'd be on 16 cars already if anyone with moral and power vetoed the fact that someone on the grid has a 4-car team that fires the 3rd or 4th driver if they fight the A-team when they're not supposed to.
And finally, Bernie should realise he has a problem if the third best team last year only managed to add Rexona and maybe a minor sponsor more. Or when McLaren gets a new exciting engine partner and a top driver, and decides not to terribly undersell its space on the car... for the second year in a row. It is very possible that Renault made more money out of sponsorship in 2005 than perhaps any non-Ferrari team in 2015.