Unlike the authors, I'm not completely confident in an MP-E macro replacement for the R series. This was always an amateur-market targeted lens. The old MP-E can still work with the R system using an adapter, which is fine for some folks. The EF lens is easily surpassed by several third party solutions as well as microscope objectives--the former lower cost and sometimes also better, the latter yielding highest image quality at 2.5X and 5X. These market changes may have eroded potential sales.
However, there is enough Canon ownership to possibly justify improving upon the lens and releasing the improved design. Releasing one with a compatible Canon stage capable of reliable .5 micrometer linear motion might help. But otherwise I'm not sure where the value-added comes from, as I'm not convinced improvements in image quality are alone sufficient to justify an R-series replacement. The convenience of the mount is something, but this isn't going to be an autofocus lens.
With respect to the TS-E lineup, I hope the lenses have barrel-based shoes for tripod attachment. While the ROGETI products are pretty good, an integrated foot is easier to use and the lens in this case should be attached to the tripod. I welcome the autofocus for improving pace of work in the field--anyone finding it less valuable can certainly turn the switch to 'off,' so I think it adds substantial value to the lens (especially since aging eyes become less able to discern sharpness in the field).
What surprises me sometimes is how Canon often skips opportunities to add simple value to their products or sell secondary products. Tripod feet for the TS-E lenses, Arca-Swiss style feet for large L-lenses, and no camo paint on wildlife lenses are possible examples of opportunities missed. A 1.4X 100mm macro represents an opportunity taken, as do DS elements. Canon has recently added more features to one-up their competition on several products and leverage their market position, but there still seems to be plenty of low-hanging fruit.
