It would be one generation too early for the 4cyl. in the entry level M car in my eyes:
-a lot of potential buyers (not only the enthusiasts) want a bigger engine and will not accept a heavily turbocharged 4cyl. at the moment
-at the next generation of BMWs (starting with the upcoming 7 series) we won't see a 6cyl. below the 3 series for sure and even a 3cyl. is considered for the 7 series so the time has come when only mpg, co2 etc. count and what engine produces that is regardless. Most of the young upcoming buyers don't care about the engine anymore even at this time, these numbers, image and design only count.
...whatever, BMW knows exactly what it's doing, what we can see in the next generation 1 series after the F2X, maybe it's really the customers fault if most 1 series owners really don't know and don't care whetever they have a RWD or RWD under their ass. (I can't believe that..)
So maybe BMW know most potential M2 buyers don't care about the engine at this time too... no dogmas right?
The highly appreciated 1M has proven that people want a combination of a small car, big engine (for this type of car and for these days), good chassis, manual transmission (beneath the automatic of course..).