I love the theories on this thread!
Thinking about the plans for future handmaids / rules around young women, I had sort of thought that the Gilead architects hadn't really thought that far - or at least they aren't allowed to say that they have.
So for the "true believers", the fertility problems were related to the sinfulness of what society had become. So by creating Gilead and perhaps having a "first generation" of handmaids to start the new generations, there would be no future issues. Nick's wife would be expected to be fertile, as would any future children. Because they now live in a Godly society.
However my feeling is that actually the bulk of even the powerful people in Gilead don't really believe in it from a biblical perspective (hence Jezebel's etc). It's all about personal gain. So while no-one can officially say that there are plans for long-term infertility because that would be publicly doubting the success of the regime, I think it's true that they'd restrict rules so there are more "sinners" - however no children would actually be "raised" as handmaids.
I find it interesting how much in Gilead is unsaid. No-one trusts each other.
I also suspect that Nick won't want to have sex with Eden, he looked pretty horrified. Will she therefore suspect him of being a "gender traitor" and report him, and will Serena/June come clean to protect him?