Most likely the tax system will be abolished and instead
replaced with a pcity upkeep cost. The terrain the pcity
is built on (and surrounding terrain) then provide income
towards the city's upkeep, which is why placing a pcity
in the middle of a barren desert may not be a very good
idea.
Naturally, if the income generated by the city itself is
not sufficient to cover the upkeep, the players will need
to shell out the additional cash. Most cities though
should be quite ok (some might even make money) based on
the income they generate. Think of this as a Civilization
ripoff
-- Gore