Yeah, I agree with this completely. My only concern is that ts% is strictly a statistic based off of shooting efficiency, and I think adding TO's would digress from that.
Either way, I think a statistic using your idea would be a valuable one.
Well, those two stats would simply measure different things, right? One would be more of a "pure" shooting efficiency stat, and the other more of an "overall efficiency per offensive possessions" stat.