"
Rumours suggest that the next M3 and M4, launched later this year, will be available in both rear-wheel drive and 4WD versions"
Like I said...nothing confirmed yet for 4wd for next genM3/M4.
What does seem to be clear is that the next generation M3/M4 will have a 500hp twin turbo inline-six cylinder engine. The new engine has just debuted in the new X3M and X4m which will be Competition Pack spec only in the UK (which incidentally, doesn't come with a switchable 4wd system, so it is not a dead cert either for any M3/M4)
https://www.autocar.co.uk/car-news/new-cars/new-bmw-x3m-and-x4m-get-503bhp-competition-version