24 TS-e with a 2x... (is it possible? the F-number won't be too good in less than bright conditions)
I've used my 17 TS-e before with my 1.4x and it works good.
Back to the question, I think you should wait for Canon to update the 45 and 90 TS-e lenses.
I tried the 24 TS-E II with Canon 2x III, and the combo works. Unlike with other Canon lenses, the 2x III does not automatically lose 2-stops of light with 24 TS-E, or at least the body still indicates f3.5 even with 2x III on. Exif data reports 24 mm, not 48 mm, so the body is likely not even "seeing" the 2x III, and the exposure is a little off with the 2x in there, which is easy enough to correct in post.
I wish Canon would hurry and release the next gen 45 and 90 TS-E. If the new 45 is as sharp as 24, it would likely just stay on my body instead of my 50L. An added bonus would be f2.0 or faster, but that's probably asking too much..