We are aiming at the same goal but having different views on the situation. I'm using the 100-400 for travelling (actually very important for me) and was hoping for a new smaller/lighter RF version but no loss of aperture. RF design makes that possible, that's the great about it. Making a lens lighter with loss of aperture, is not a game changer, not much innovation needed for that. And it's not even the same lens anymore. I would even be OK with a lens design change like in the case of the 70-200 loosing internal zoom.
For hiking we will have a very portable 70-200/4 which everybody will love I guess. I would definitely buy it hadn't I tried the 100-400 on my last backpacking trip. Kills my back and makes me sweat but I just can't live without 300-400mm anymore.
I don't need the extra 100mm in the 100-500 tho and a weight/size reduction on the 100-400 without loosing aperture would have been my wish.
I guess a 70-200/2.8 style 100-300/4 with external zoom optimized for size and weight would be my dream travel lens. Accepting teleconverters of course.
Please note that justifying lens aperture loss with higher ISO is not valid imho. Aperture changes DoF which make it a different image. You can't give a painter lower quality paints and tell him he has better brushes to compensate.
I don't think an L 100-400 with the same parameters as the EF would be significantly lighter. I rather have the 100-500 which is actually lighter than the EF 100-400 but gaining extra 100mm than an RF 100-400 which is 1300g instead of 1400g. Just shame for the huge price increase.