Clubs won't get affected by this rule, club owners are one of the richest businessmen around who've invested millions on their clubs already. They've got armies of lawyers and accountants that will find loopholes in that rule (some like city already did).
Anyone thinks otherwise is pretty much naive. It's that simple.
I think UEFA will cave on their FFP initiative simply because they would be shooting themselves in the foot by banning poorly run clubs, as these teams attract the most people/$$$ (Chelsea, Barca, Milan, etc). Not to mention it would exacerbate the situation of those clubs by denying them CL revenue.
I don't see them having that problem with City though, whose absence from the competition would not cause that much damage in comparison to teams with much larger global followings. A club like Liverpool will continue to have many more supporters worldwide, despite City's surpassing them over the past few seasons.
As for those discussing debt, it is not so much an issue or size as it is being able to carry it. A club like Madrid won't be banned because they can still service their debt and break even. Such is the size of their revenue. One of the advantages of being 1 half of a TV rights monopoly and a guaranteed top 2 finish every season.