If you want to do something like that, I would just give one extra horse (like how kush gets a healer at the start) and keep the starting 4 women. Unless there is good hunt, the proposal will really slow down Persia's boom, which is already slow. For reference, a simple test shows that the proposal will result cause to already being 20 seconds slower at 20 pop (and that one extra cav unit will be a drag on the boom). With the proposal, I suspect no one would ever play Persia in team games because they would be too slow.
In other words, 4 starting women and 1 cav can make an extra cav unit and still be about 20 seconds faster by the 20 pop mark. So 4 starting women is always superior. If there isn't extra hunt (i.e., no need to make a second cav unit, then 4 starting women will become much, much faster