CD Embry: +1. I agree about the sharpness of the 90 TS-E, one of my favorite Canon lenses. While the sharpness would be very hard to improve, they might make it focus closer, apply their more recent and better lens coatings plus the independent movements of both axes, as in the recent 24 and 17mm lenses.
The 90 TSE is almost perfect as it is, with the possible exceptions of the suggestions as listed above. But, they could really hit the mark by adding to the TSE line for product shooters, by making either a 135mm, 150mm, or 180mm TSE as well. This could be the other "specialist lens" mentioned. It would be perfect, especially the 135 or 150, for products that required some distance from the camera to make perspective look more normal, which the 90 barely does in some cases, not in others. To shoot a low front 7/8 view of a car, for instance, looks a heck of a lot more natural (i.e., the front end doesn't look quite as exaggerated in size compared to the rear) and just plain better, with a lens longer than 90mm. A longer TSE would complete the set for product and other types of photographers who would then have almost all the lenses with almost all the tilt and shift functions they needed to function as did their old 4x5" and 8x10" view camera set-ups in the film era - a great advantage for Canon over even medium format competition. Finally, if the much rumored studio-centered cam with very high megapixel capacity came out about the same time, that would further seal the deal for many commercial professionals who now are still somewhat married to the necessity to maintain various systems, jury-rigged together, to satisfy different types of shooting requirements.