I'm totally ignorant on these matters so could people enlighten me: why a 28 as well as 24 and 35? Is that a gap that needs to be plugged?
Historically, it's more of a Nikon thing. Canon were the first to create a 28-70mm f2.8 L way back. It was a massive seller and most pro's had one as their main goto lens.
Nikon eventially released their version after a long wait...and just after it was launched, Canon dropped the worlds first 24-70mm f2.8 (which we all take for granted). Again, this became a massive long time big seller for Canon. Nikon users were "happy" with their 28-70/2.8 (which was a fine lens). A lot of Nikon users got used to the 28mm view point as being their wide option. Back then no one bothered with UWA lenses...you had to be wealthy or had a very specific photographic need for a 16-35mm lens.
Nikon eventually released their 24-70/2.8 and with their recently adopted CMOS sensors...a lot of wedding photographers jumped ship because this new Nikon lens was a lot sharper at 70mm than the Canon version. Nikon didn't have many super fast primes (unlike Canon who had 24mm f1.4, 35mm f1.4, 50mm f1.2, 85mm f1.2 and 135mm f2.0 options). The only fast primes they had were the 28mm f1.4 (see a common trend there), a 50mm f1.4 and an 85mm f1.4. There wer fine lenses but their AF was very dated and slow compared to the far more modern lenses that Canon already head. Around 2008, Nikon launched a range of f1.4 glass to match Canon's offerings.
In Nikon world, there's a lot of photographers who like the 28mm perpective. In the Canon world a lot of mediochre consumer zoom lenses started at 28mm. So this particular view point wasn't generally as appreciated as it was in the Nikon linage. So i don't think there will be a lot of Canon enthusiasts picking up the new RF 28mm f1.4. Especially if they already have a suite of fast EF primes. But if you are a Nikon enthusuast who's about to re-transistion back to Canon...it makes a lot of like for like trading sense.
For years I used a EF 28-135mm f5.6 IS and was really happy with 28mm as my widest option. It wasn't until I started to shoot weddings that I bought a 24-70 f2.8 L and realised just how useful those extra 4mm were on a standard f2.8 zoom. In the early days of digital (I had a new 300D) I bought the first copy of the Sigma 12-24mm f5.6 HSM in the county...on my Eos 33 film camera it was OMG wide. On my 300D...it was nice and wide! When the 5D finally dropped, I was one of the first in my area to buy one because I wanted the full frame sensor...and my 12-24mm lens became my OMG lens for many years.
