Both Islam and Judaism deny Christ, so I am not sure how the differences could actually be handled over time with a husband of the Christian faith. Same goes for New Age, or what I have come to understand is marked as 'Spiritual' on this site. Core beliefs matter. Being unequally yoked does have consequences.
The idea of differences in religion is not deep enough, what should be discussed is the idea of beliefs of the heart. What does someone truly believe when it comes to family, relationships outside the home, the world in general.
A family that is already established based on the beliefs of the 'family' risks being changed by the beliefs of someone coming in. A husband may think he can deal with that difference but the thing that may need to be consider is how will that difference effect the other members of the family's belief?
The method of morality most be defined within a family, is it from an external absolute source, or is internal based on what society, or each individual dictates? I know from the statement you made about the three man made religions morality is not as much an issue as it would be for someone outside those beliefs.
In any event, even though I don't think mixing of religious diversity within families is a good thing for some, all depends on the family structure and what they are willing to allow.
However, I think plural families need all the help they can get from the community of poly believers and so accepting poly families outside of religion is beneficial to all.