This is an amusing liberal fantasy, but is it really practical? Probably not.
If Bloomberg or Steyer (or Bloomberg and Steyer as a partnership) buy Fox News, and tell their employees to run a real news outlet instead of a right-wing propaganda mill, what will Fox News’ talent do? Some of them might comply with the new boss’s orders, but many wouldn’t.
Murdoch would be flush with cash thanks to the transaction, and use it to start a brand new right-wing propaganda mill. (The market viability of such things has already been proven by today’s Fox News, of course.) The disgruntled talent from the old Fox News would jump ship to the new network, as would the audience for that talent.
It would all amount to nothing more than a very expensive game of Whack-a-Mole.
Mind you, there is a problem with Steyer and Bloomberg using their money to run as primary candidates, and there are much better ways that both could be spending their money, but buying Fox News is not one of those ways.