I would be happy with your 15% off the RF 100-500, I bought mine in the 20% off sale afterwards and I'm still waiting for it (back-ordered from Canon). My order was placed back in October 2020. Although I'm pretty happy overall as all the other RF lenses from the same order arrived quite some time ago :-DHappy to be an early purchaser of the R5 albeit at a premium price. I did get a bundled spare battery and sold the strap so some discount overall. Deposit was down with digidirect in Feb 2020 as I expected to go on a Scandinavian/Iceland holiday in July which didn't happen.
I had included the RF100-500mm in the R5 pre-order but cancelled the lens as it was just too much especially as the R5 was more expensive than I had budgeted for.
In September, I pre-ordered the RF100-500mm when they had a 15% off sale and got it 2 weeks later! I missed the 20% off sales but also got the RF70-200mm @ 15% off. Happy camper overall
I don't have any compelling reason to buy another RF lens in the current lineup. Even a RF replacement EF16-35mm/4 or EF100mm macro couldn't be justified at this time. If my EF24-105mm/4 gets broken then the RF version will be perfect though.