
Curved Mullions are no longer an issue in Revit!
(SECRET REVEALED IN COMMENTS BELOW)
They are easy - you simply select the 'curved mullion' checkbox on the Options Bar when you are placing curtain grids. Shape handles allow you to pull and push manually or you can enter the radius in the field. Floating Mullions (not attached to the curtain wall edges) must be selected PRIOR to adding them... meaning you can't convert one of the simple curved ones to a floating mullion.
Finally we can do anything we want in Revit!
If you need any help with this just email me here at BIM WITS!
Happy Curtainwalling....