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Microsoft are legitimising bash as an OS feature for "developers who like unix".You are imputing far too much power to Microsoft. It's Linux operating systems that have "legitimized" the Bourne Again shell as an operating system feature, long since and with more clout than Microsoft could wield in this regard.
As such, if Apple can stand up to the "pressure" from a quarter of a century of Linux operating systems, several of which are no longer "bash everywhere" in any case, it can stand up to any pressure that the Windows NT Linux subsystem could possibly exert.
Anyway, "developers who like Unix" hopefully also like its long-standing notion, going back to the 1970s, that there is not only one shell. Thompson, Bourne, Almquist, C, TENEX C, Korn 88, Korn 93, MirBSD Korn, Bourne Again, Z, Debian Policy-compliant, Debian Almquist, Friendly Interactive, Yet Another, ....
Given that this new subsystem is touted as giving developers the means to run Ubuntu toolsets, it behooves us all to look and see what Ubuntu (14.04, the same as in the demo video) actually has when it comes to shells:
* http://packages.ubuntu.com/hu/trusty/shells/