It doesn't sound like they declared 20mp as a 'limitation' as such. They said it was 'sufficient' therefore Canon has decided to aim for that one stop of high ISO performance over an increase in MP as well as reducing the strength of the AA filter(which will effectively give a resolution bump over the 1dx2 anyway) as an increase in MP was not deemed necessary for the target audience.
I was torn between going for higher resolution via 5D4 or 1 level camera via 1DX2. It went on for weeks and finally my wife nudged me over the edge - she sees 1D as "the best". Essentially it was a coin toss. To compensate for no bump in MPs (sold the 6D) I bought the 400 DO II, really over-spending and rationalized that 400 X2 based on reputable comments would be very satisfactory. Truth is, 800 did put me within reach for a lot of birding situations but as more samples of the results of high MP shots passed by me I came to realize that my cropping capabilities were now more limited if I wished to maintain the detail and sharpness I was accustomed to (I had previously used the 300 2.8 II, which uncropped was amazing).
As a retired person and just an amateur photographer what in the world is wrong with me not just being satisfied with what I've got?! Well, the problem is I tend towards being a perfectionist; nothing to do with showing off, I just love excellent results. Honestly, I can't afford this hobby but by cutting out other likes, I do, and I really enjoy it.
With over 3 years of fun with the 1DX2, I've absolutely loved the 14 FPS and the 4K60 and could have been quite happy with a boost of 4 or slightly more MPs and in that case jumped on the expensive 1DX3 bandwagon. Others say no, but I maintain that often I'm on the edge, where cropping that would be offset by those extra MPs, would be very much appreciated. Perhaps by analogy it could be compared to having a car that tops out at 55 when speed limits are 60.
On the other hand, talking about being on the edge, recently in Costa Rica, I was reminded what it was like to have roughly 12 hours of light and dark and mist and deep shadows in jungles and, well, there is no doubt that low noise higher ISO would have been really helpful especially when I was at F4 X2. In many of those cases my reach with 800 (560 probably would have worked too) was fine but the lighting just wasn't there.
So, which poison do I choose. What I'm reading about the 1DX3 resonates because I am very aware of improvements that could be game changing if the reports are trustworthy but would I ever be happy with just 20 MPs. Anyone else feel like me, or share the same thoughts?