The real limiting factor for megapixel count in sport bodys?

Cryve

EOS 80D
Jul 4, 2018
105
67
Germany
So far almost every sport camera kept the megapixel count to arround 20mp no matter if fullframe or aps-c.

Now with the 7d III slowly apporaching release im wondering what is actually limiting a sportsbody to go to higher megapixel counts.

Previously it was assumed that the megapixel count affects low light performance. The lower the megapixel count, and therefore the bigger the size of the photocytes, the better the iso performance.

Recently i came across some articles that discussed that the megapixel count only really affects the per pixel performance, but the overall iso performance of a picture, scaled to the same size, basicaly stays the same with increasing megapixels.

Thus it seems that the only limiting factor is data thoughput or perhaps sensor read speed?

Does anyone here have insight on this? could we, given current technology, however unlikly, see a 7d iii with 26 or 28 mp and about 12 fps while still providing an improved iso performance?