Believe it or not, we aren't that far from having this happen.
Believe it or not, there are now just as many BMWs that are available as M models as those that aren't. In the US, we counted seven models that have an M variant including the 2, 3, 4, 5, and 6 Series and well as the X5 and X6. The same number of models, the X1, X3, X4, Z4, 7 Series, i3 and i8 models are not available as M models. BMW has plans to expand its range of M models to compete with Mercedes which has AMG versions of almost every one of its cars. So let's take a look at what BMW would have to do to make an M version of every model.
We know that an M7 is off the table, so that leaves four possible M models for BMW to build. We don't see the point of an i3M and the Z4 won't be around much longer, so they too are eliminated. That leaves just the X1, X3, X4 and i8. An X3 M and X4 M would be simple enough to build. By putting the M3's S55 engine, making 425 horsepower, into the X3 and X4, M variants of these models would be pretty sweet. Things get a little tricker with the i8. A mid-engined M model would seem like a no brainer, but BMW can't seem to make up its mind on the i8. The i8's goal is to be fast, but efficient. Replacing the three-cylinder engine with something from the M division might ruin the car's mission.
We would actually really like to see an X1 M. The upcoming 1 Series is based on the X1's platform, so a new 1 Series M could share an AWD platform with the X1 M. These cars would be powered by a four-cylinder engine making around 360 horsepower. The X1 M and 1 Series M would be good rivals for the Mercedes GLA and CLA 45 AMG models, respectively. Finally, the upcoming Z5 convertible will probably get an M model. The Z5 is being co-developed with Toyota and little is known about what will power it. Some rumors claim that an M variant could be a hybrid with around 600 horsepower. It is amazing that the M division has grown so much in recent years.
Some brand purists may be angry that the M brand is being diluted, but it seems to be working well for AMG. We can't complain about BMW offering more performance models. It is very cool to think that building an M model of almost every car is not far from actually happening.