I think it's a horrible decision. I'm freshly divorced and I blame it in part to her being a stay at home mom. As others have said, she'll miss adult interaction throughout the day. She'll come to resent that you can step away from parenting during the day, while she can't. She won't want to ever hire babysitters, because she'll feel guilty having to hire babysitters while she is a stay at home mom. When you come home from work, it will become your turn to spend time with the kids while she goes to visit friends, run errands, or do things separate from the kids. Eventually you'll be parenting the kids separately, as a means to give her some personal space. That stuff collectively builds.
(And then you'll get a divorce, she'll get a low paid job, and complain that she now doesn't have time to do anything fun with the kids.)