First of all, what about fathering? Why should fathers not be remunerated just as much as the mothers? How does it promote gender equality to suggest yet again that everything that has to do with children is exclusively part of "a woman's world"?
Another question is why society should pay for this particular personal choice and not any other. How about people who choose not to have children? It can be argued that their service to society is greater since their decision reduces their carbon footprint and helps combat the horrible overpopulation that is the scourge of this planet. The argument that is often made to counter this statement is that society needs to have taxpayers, which is why people who have children perform an important service to society. If that were the case, however, we could simply legalize the 12 million illegal immigrants and get them to pay taxes. This would have the added benefit of giving us 12 million of fully grown adults who are ready to start paying taxes right now and who don't need any investment into their schooling.
Feminism has fought long and hard - and the battle still continues - to promote the idea that having children should be a matter of personal choice. In developed countries, women are not forced to give birth against their will. However, choices bring about responsibilities. If you have made an informed personal choice either to have or not to have children, why should you expect other people to pay for it? If society is paying for motherhood, should it also not be able to enforce it?
If "mothering is a form of labor," women should be prepared to be treated just like any employee. To give an example, as an employee of my university who gets paid for her labor, I don't get to choose whether I come to work or not. I am also obligated to perform a long list of duties that are specified in our faculty handbook. Should I fail to perform those duties, I will be fired. If mothering starts being treated as labor that is performed by women as if they were society's paid employees, will they be handed out a handbook of rules right after they give birth? Will they have to file regular reports on how well they performed their duties (which I am, for example, scheduled to do at my place of employment in two weeks)? Should they be fired from motherhood for failure to perform their duties as specified in a long checklist? Will we see "mothering contracts" that society has to renew every year just like my university renews mine?
Most importantly, has anybody asked women if they want to sell their freedom of whether to have or not to have children and how to parent them to the government?
If we want feminism not to become completely irrelevant to the mainstream population, we need to start being very careful about such supremely misguided suggestions.