I think that a womens only class would be alright but I think perhaps it should be something a womens support group organizes, not necessarily a regular aikido class in a dojo. Probably most dojos wouldn't have enough women interested in such a class to warrant having one, but I don't see a problem with a support group organizing one. They could either run one temporarily in a dojo or invite an instructor to come to them, if a dojo couldn't accomodate them. I don't think that it would do much good unless they eventually joined the regular classes.
Personally, I still find most men intimidating to work with, maybe I always will, but I am learning to work through it and that is something I would never learn to do in a womens only class.