I think it's less Moffat having a problem with women writers and more that he's gotten attached to a handful of male writers who already know the style and technique of writing for DW.
And as others have pointed out, Moffat has certainly had no problem with women producing and directing the show. So it seems highly unlikely he would suddenly have a problem with women writing an episode as well.
I think you may have a point there with him sticking with an established pool of writers. Another sign that he's over extending himself?
Not really. Out of the nine writers this season three are first-timers, with four writers with previous Who experience other than Moffat himself.
Since this year is Moffat's fourth season, let's compare to RTD's fourth season, which out of seven writers had two first-timers and four writers with previous Who experience other than RTD himself.
So in their fourth seasons Moffat's staff is 55% familiars 33% newbies, while RTD's staff was 71% familiars and 28% newbies.
Hmm, for the fun of it, let's compare season 2 and 3 with seasons 6 and 7. I'm leaving out seasons 1 and 5 since season 1 would have 100% newbies and would be disproportionate.
So, season 2: 7 writers, 3 experienced (42%) 4 newbies (57%)
Season 6: 8 writers 6 experienced (75%) 2 newbies (25%)
Season 3: 7 writers, 3 experienced (42%) 4 newbies (57%)
Season 7: 7 writers 6 experienced (85%) 1 newbie (12%)
Hmm, so at the end of this exercise we learn that despite this season, RTD did more of an effort to bring in new blood than Moffat has. Fun exercise, though.