This lens looks tempting but I'll pass. My reasons? I sold my EF 14 f/2.8 II and my EF 16-35 f/4 then got the RF 15-35 f/2.8. Even though the lens listed in this topic might be lighter than the 15-35, the lens I got replaced two and does not need an adapter so the weight reduction in my bag is significant. Plus, the RF 15-35 f/2.8 can accommodate an circular filter (I have some 82mm filters from other lenses already). I really do not need to go to 14mm for what I shoot. And, at 15mm, lens coma actually seems better than the 14mm I sold.
I think if I was looking for a wide lens as an initial purchase, I might go with this to complete a triad of f/4 lenses (70-200, 24-105, and 14-35) but, for me, my choice made sense.
For you it makes a lot of sense to use the F2.8 and yours reasons sound very plausible. I had actually decided to go with the RF 14-35mm F4, but now after I read your post, I'm torn/ tempted again to get the F2.8 instead.
Advantage F2.8:
- great Astro lense
- better for city nightscapes
Disadvantages F2.8:
- need to carry an adapter ring for filter thread
- possibly heavier
- "upgrade" is very expensive for little use...
- landscapes mostly shot in lower apertures --> F2.8 is overkill...
Advantage F4:
- probably lighter, smaller
- filter thread 77mm
- hopefully much cheaper
- 1mm wider
Disadvantage F4:
- low aperture for astro... (a tracker might help...)
- I might need another lense for astro... more weight when traveling
As mentioned, these are my personal pros and cons. If anybody would like to weigh in, please. Tips are always welcome

especially if you're experienced in astro photography with these two apertures because that might be the decisive point for me.