[Brightcolours]

The 100 mm macro, as before, is not a 100 mm lens anymore when shooting macro. Focusing distance at 1:1 is 28 cm (object to sensor) and 26 cm at 1:1.4.

That means it is a 69 mm lens at 1x magnification and 65 mm lens at 1.4x magnification. This means I will certainly not get one.

For those who like to shoot video this behaviour may be beneficial, as it may have little to no focus breathing at normal shooting distances.

Yeah.. about that.

You got those numbers from dpreview?
DPReview says 26cm MFD (1.4:1), 8.6cm working distance. 

The lens is internal focussing, as far as I know. 

DPReview says 28cm object distance at 1:1... So they gain 40% magnification with 2cm of movement (or to put it more clearly.... they gain 40% magnification with going only 7% closer to the subject)? And they say 11.2cm working distance at 1:1.
26 - 8.6 = 17.4cm
28 - 11.2 = 16.8cm.
Something is off with those DPReview numbers, and your calculations.

Canon states 26cm MFD and a lens length of 14.8cm. The RF mount has a 20mm flange distance. 26 - 14.8 - 2 = 9.2cm working distance instead of 8.6cm. So DPReview's working distance figure for MFD is wrong.

Can you point me/us to a Canon subject distance number for 1:1?

Anyway. You say you will not get one. You won't be getting the Canon EF 100mm f2.8 L USM then, either. It does 1:1 at 30cm MFD (this RF lens does 1.4:1 at 26cm MFD). Or the Canon EF 100mm f2.8 USM. It does 1:1  at 31cm MFD. Sigma's new 105mm f2.8 DN ART? 1:1 at 29.5cm MFD....