No I wouldn't do it. I know it can be nerve racking to know you are going to be getting a horse soon and you want to get as many things as you can. Helps take the gitters down to go shopping ;)
Each horse has such a different conformation from another one of even the same breed that I would really discourage buying a saddle before the horse. It is a very significant amount of money to spend therefor should be done properly.
When you say near future, how soon do you think you are going to be getting one? What breed?