I didn't think it was a stretch considering the e60 indeed was designed and built for using a SMG. The manual was an afterthought due to the american market demand and then yes of course they tested it but was not their goal to even offer it and many press releases said it was made to work with smg
Considering the powerplant in the m3 is designed off the s85, it is not unfounded to think the smg/dct also is a better fit in terms of delivering the engine power most consistently in its powerband. Again the market pressure of america makes it not even a consideration to no longer replace it.
But why is this so far off considering what happened with the e60 m5 and how they designed it for SMG. Not sure why its so far fetched to think a similar mindset came to the m3 as for them its about how to make the car perform the best, which dct/smg allows it to do