"As man now is, God once was;a doctrine held by Mormons?
As God now is, man may be."
The answers Mr. Mouw has received varied, depending on whether he was in ecumenical dialogue with Mormons, or hearing from people convinced Mormon belief is incompatible with Christianity.
Among related items, First Things published some Mormon apologetics by Bruce D. Porter and Gerald McDermotton on the topic
Is Mormonism Christian?* in the October 2008 issue, and one Mormon's post on theory versus practice, Ralph Hancock on
Our One-sided "Openness" to Continuing Revelation in October 2013.
*Richard John Neuhaus dealt with this same question in his The Public Square column in the March 2000 issue.