Seconded on this. The 2.8 70-200 doesn't take extenders in exchange for portability. There's no way that they would make the more portable 70-200 F/4 less portable than its bigger brother. That is, unless they decide to make the more expensive 2.8 lens more portable than the cheaper F/4 lens to convince more people to upgrade.
I love my RF 70-200 and honestly that lens on its own has been such a huge change for me. My go-to set up at the moment is the 1DX2 with a 24-70 and R5 with the RF 70-200, and it really just feels like I'm carrying two 24-70s. Way, way more comfortable using the RF 70-200 on the R5 than my old EF.
Nobody seems to be bothered to look at the RF 70-200mm f/4L IS patents. There are two, and
both are Internal zooming.
f/2.8 length on the patent: 172.73 ~ 219.96 ~ 231.71
f/4 length on the patent 202.98 ~ 202.98 ~ 202.98
The 20mm flange distance needs to be subtracted from these.
So not a huge penalty in terms of size, still smaller than the EF f/4 versions with an RF adapter.
Either pay a premium for f/2.8 and reduced length or pay less for f/4, internal zooming, and teleconverter compatibilty. (Until they come out with an f/2.8 internal zooming lens, if they ever will)