Brunswick And other old time manufacturers used to make shafts with ebony spliced to the nd of the shaft and as I recall, they played fine but the cues were typically heavy, 20+oz to offset the weoght of the ebony.
As far as making one entirely from ebony, it would weigh between 7 and 10 ounces and wouldn't play as well as maple. I've built purple heart, piquia amarello, ash, and birch, and cherry shafts over the years and nothing came close to maple.