If they have a zip or snappers at the bottom and are in plain colors I may get one, handy for letting the dog out in the middle of the night. As for farmers if they think that (a) they are a bargain (b) useful, they will queuing up to get them (or probably getting their wives to get them).
You don't need snappers at the bottom to let the dog out in the night.
If he get's too warm in there with you just let him out of the zip on the front.
Although I question how hygienic it is to share a onesie with your dog anyway?