Like I said it depends on what line (classics or masterpiece) you want him to fit into. I also imagine that how big he is affects his detailing, articulation, joint strength, etc. all factors that need to be considered. If you decide to make him bigger, does that mean that you have to do some redesign?
As for sizing, 10 inches is a good size for him to fit into classics. However it is too small for MP. 12 inches would be a good MP size. And no matter which line you pick, if it is a great product, it will sell.
And something to think about with your thread over on TFW, all the requests that are being made, are they from the vocal minority? Because remember, if it is the same 10 or so people telling you how this toy 'has' to be, they are not necessarily representative of the majority of your market. By catering to their personal preferences, you may be excluding a greater number of people.
Just some food for thought. :)