Canon RF 8-16mm f/4 sounds good, better than the other patents starting "only" at 9 or 10mm and will fill the "gap" for some extreme/insane UWA .
It should pair well in a kit with the existing Rf 15-35mm F2.8 or the future (is it confirmed?) RF 14-35mm F4 for "normal" UWA
If the Canon RF 1200mm F8 Canon is coming, an ultra wide angle starting at 8mm doesn't seems insane anymore, more extreme focal lengths need to be available for the RF mount, smartphones are already getting insanely wide lenses, 8mm rectilinear will put interchangeable lens cameras at the top again, Canon needs to make a number of lenses that no future smartphone camera in the next 10, 20 or even 30 years could challenge, any future customer of RF cameras will have a smartphone and if a good lens is already inside a smartphone less people will want to buy a mirrorless camera if there isn't a huge and evident advantage, the challenge is not (only) against Sony or Nikon anymore, but against Samsung or Apple smartphones, sure till now no smartphone camera is as good as any modern miorreless camera, Canon (Sony, Nikon, etc ...) need to push the boundaries to keep this advantage even with some insane lenses, just to mark the territory
8mm is almost as impractical as 1200mm especially in a smartphone, but the few that want this kind of challenging focal lengths will love to use a proper camera to make this lenses useful for their creativity, this is the mindset that Canon engineers are probably using, also F1.2 lenses or F2 zoom are the sign of this trend, if a lens is too "extreme" to be available in a smartphone it's a good lens that will differentiate proper cameras from phone cameras.
Even if I could be happy with "just" a 15mm or 14mm wide lens and a 500mm or 600mm tele, I'll like to be able to rent or buy something much longer or extremely wider if i feel I need to expand my creativity.