Of course I had to buy the EF 16-35 f4L IS a few months back to go with my control ring adapter and EF 100mmL. I had found a Like New 16-35 at KEH for $700. But this RF lens was what I wanted. I would look for that lens to retail at $1599 at most, with $1349 being my final guess.
I live in deep poverty, but I will definitely be after this lens, after using the RF 85mm f2 and discovering that focus peaking turns on as soon as you take over focus after one-shot AF. With EF lenses the focus peaking only works in MF. Also the EF 16-35 is HUGE on my tiny RP. I use the 16-35 for street photos, so smaller lens is great. (Please Canon, make a 28-35 f2 for my street work!!!) The EF lenses are fantastic on R bodies, but the RF lenses offer more features, even IF you have the control ring adapter.
So I am very excited and glad that this is finally coming out. I want the f2.8s and the f2's, but I can't afford them. The R5 and RF 50L broke me for months.
So looks like I will be selling my 16-35 this year sometime...unless I hear a good rumor about a 24-35mm lens, I am all in on that zoom.