I could get quite a lot of use out of a true 24,000-speed film. I am interested.
I have already shot 400X, and it is amazing all right. I have not bought it in any quantity, because I still have some Provia 400 that I need to polish off.
Yes, it's a shame no sheets sizes in 400-speed transparency film. It would be my ideal color film for almost everything I shoot in sheet sizes. I use 400NC now, as it is my only choice for ISO 400 in color, but I really do not like it very much, and I think transparencies give you so much more control. 4x5, 5x7, and 8x10 would be a good start.

Then, after we here at APUG wow them with our buying power (HA!), they will introduce larger formats.
I would also like a super-speed transparency film (again). A color equivalent of Delta 1000. 1000 speed, flat, grainy, incredibly pushable.