Wouldn't that be unfair to teams that decide to sell off all their players and rebuild? A decent top level team might be able to gather 10m for their players. If you managed to train up a few rare high value talents and sell for 3m+ each, you'd have to be careful if it was a hard cap that would eat up any excess.
I agree with chihorn that its a symptom of a bigger issue. The ability to generate lots of money through tanking or operating a team in the very small countries should be addressed. I assume a team would be able to sit in the bottom division of their country and train cycles of players for a huge bankroll as well.
I'd suggest they focus on balancing out revenues and expenses instead of putting any sort of cap on cash or payroll. Seems like they are attempting to do this for tanking teams. Small countries with very few managers is still an issue, but that's a much smaller global impact.
"Well, no ones gonna top that." - http://tinyurl.com/noigttt