I shoot wildlife and larger birds (eagles, etc). Currently using two R5m2s with the 100-500 and 70-200mm f2.8 Z. The 100-500mm is my workhorse and I really love this lens. But I want to upgrade to faster glass and the extra 100mm of reach. I really want the improved Bokeh and low light advantages of faster glass.
Looking at patents is fun, but unrealistic. Apparently, the patent for an "L" series lens is rarely released ahead of the lens. Canon should update their EF 400mm f2.8 and 600mm f4 lens adapted to the RF mount, soon. Nikon released their 400 2.8 with the teleconverter in 2022, which is very popular due to the increased versatility and convenience. Actually, both Canon & Sony have done nothing to respond. I will be amazed if Canon updates their 400 & 600mm without built in teleconverters.
Yes, I have been envious of Nikon's long glass options, but not their cameras (my opinion). I have considered buying a Nikon long glass setup. I've debated the old EF 200-400 f4 ( released in 2013) with the built in teleconverter, but not in love with 8lb weight. It's actually pretty sad that I'm looking back at a 13 year old lens as an upgrade! I have high hopes Canon is going to wake up and upgrade their long glass options. I've watched the rumored 200-500 f4 (which I would have bought) transform into the 300-600mm fixed 5.6. In my opinion, a proposed $7000 fixed 5.6 lens is a disappointment for the money and a minimal upgrade from the 100-500. I love the versatility of a zoom for wildlife, but I've come to the realization that I need a prime. So, if they release a new RF 400mm f2.8 with a switchable teleconverter (providing 400 & 560mm like the Nikon); I'm going to buy it. If not I'll buy a used RF 400mm 2.8 and do the teleconverter juggle. There I've made a decision. Now, it's Canon's turn to release some lens in the next 6 months! I'm almost 70 years old; it doesn't do me any good if I'm in a nursing home when you finally release the lens I want!!!!