I think it makes the most sense for you to use the rooms in such a way that suits your lifestyle. A master bedroom is only a master bedroom because that is what we call it. If you want it to be a sewing room, then go for it. Particularly if you don't mind a smaller bedroom for yourself. I don't think it is weird at all and I imagine that once you do it, you will adjust faster than you think and be glad you did!
