What convinced me to go with the 24-70mm instead of waiting for the 28-70 f/2 came down to just a few things.

The 28-70 would be like having several primes, but the only prime in that range that I really use is the 35mm F/1.4L II and I like using it at F/1.6-1.8. The 28-70mm would be like a slower prime all across the range.
In older versions of the 24-70 the lens wasn't as sharp as it is stopped down, but the 24-70 II was sharp at f/2.8 and I believed the RF version would be to. So at all the other lengths the f/2.8 will be fast enough.
The final tipping straw to order it over keeping my the EF 24-70 II is the fact it has IS. Without flash shooting family pics at night the IS might be nice, and the holidays are coming and the lighting will be by X-mas tree.

How about the 100-500mm, is it worthy?
Would it be similar to owning the 100-400mm, or substantially better?