Presumably larger pixels allow for measurably better dynamic range and lower noise, both important factors for pro photographers. What puzzles me is that the megapixel race is still ongoing elsewhere even though the new top tier FF cameras remain at 24MP. The higher MP count requires more processing and more storage, not to mention much tighter lens specification, so where is the benefit?
No commercially available screen offers anywhere near 50MP resolution, so one can only see the increased pixel count by cropping the image or by printing a monster blowup at some expense. It is a puzzlement. Any good explanation apart from market competition?
The limits to adding more MP (apart from die size and sensor architecture) is processing and memory - that is data transfer internally and externally. Greater requirements here come at greater heat and economic costs. You can pretty much track increasing resolution with these drivers and developments.
With these high speed PRO machines the extra MP is all about flexibility. Flexibility to crop off centre and capture something that otherwise may be missed, or just to present the composition better.
These 2020 PRO machines will be workhorses rather than spec-sheet glamour pusses ..... the big question in my mind is who is going to come out as the AF top dog?
I can only hope such AF and speed improvements flow down to APS-C , D500S, 7D III, and a7000, level next year, as these glacial evolutions don't inspire me to carry 1.4kg of body around (actually these days I don't think anything could now that mirrorless is here - I will wait for a do it all higher res PRO FF mirrorless at about half the weight)