After my previous post, I began to wonder the same thing.
In AWB states, the previous M&P9c "1.0" required a special 10rd magazine since the its normal capacity was 12 rounds, while the M&P40c and M&P357c were right at the 10rd limit. However, it's no secret that sales of .40 S&W and .357 SIG pistols have faltered recently, while 9mm sales have burgeoned (case in point: the M&P357 line was completely dropped from the S&W retail catalog several years ago).
A smaller M&P 2.0 Subcompact tailored precisely to 10 rounds of 9mm probably makes more marketing sense than a slightly larger pistol tailored to 10 rounds of .40 S&W; it would be more attractive to buyers in restrictive states, and S&W would not need to manufacture 2 styles of 9mm magazine for the same pistol.
The M&P 2.0 Subcompact may cannibalize some sales from the Shield, but the Shield is such a runaway bestseller that S&W may find this to be no great loss in the big picture. Likewise, competing head-to-head with Glock isn't necessarily a bad thing.
On a related note, the new 2.0 9mm Compact is likely to make buyers in Colorado happy; due to that state's 15rd limit, M&P 9mm buyers were reportedly upset at having to choose between the 12rd M&P9c and having to use 10rd AWB magazines in the full-size.