I think the point is to allow Linux binaries to be used without a recompile, which saves MS most of the cost of maintaining binaries for it.

Which is the key. Plenty of ISVs make Linux binaries, but nobody was interested in Interix binaries.

Indeed. I think you can see this in some of the history in this article: Interix was "POSIX compatible", but essentially its own OS, like compiling for Linux versus BSD. So someone had to maintain binary builds of GNU tools for Interix and thus you ended up with the large "Tools" distribution of user space binaries. Ultimately, "Tools" was its own Unix distribution that was subtly incompatible with any other Unix distribution. Even today on Linux you still see a lot of the headaches in the subtle binary incompatibilities across Linux distributions.

The amazing thing with Ubuntu on Windows is that user space is the same Ubuntu distribution of user space tools as on Linux. That lessens the maintenance burden of the User Space considerably as Canonical is already actively maintaining that distribution, and will continue to actively maintain that distribution, and that there are a considerable number of users of that distribution on Linux already and a considerable ecosystem of third parties building for that distribution. Those are definitely the missing pieces that Interix never had and makes this "Son of Interix" that is Ubuntu on Windows much more interesting.

Does anyone actually care about Linux binaries? A lot of linux programs tend to be shipped as source.

Exactly, couldn't say it better! MS has a history of decisions which were meant to strangle the competition, one way or the other. Interoperability was never one of their strong suits.

Would you actually call for such a revival?

* https://news.ycombinator.com/item?id=11446694

What do you mean "call for"? In the abstract, yes. I might put a bit of personal time into it. I might even pay $30 or so for it. But that's unlikely to move the needle for Microsoft.

Instead of the wistful subjunctive ("if they had revived Interix I would have ...") something in the imperative mood.

Please revive the Subsystem for Unix Applications, Microsoft!

You own the technology. And it addresses quite a number of the issues that you are currently listing on GitHub against the Linux Subsystem. Including:

* Interix has pseudo-terminals. (https://news.ycombinator.com/item?id=11415843 https://wpdev.uservoice.com/forums/266908-command-prompt-con... https://github.com/Microsoft/BashOnWindows/issues/169 https://github.com/Microsoft/BashOnWindows/issues/85 https://github.com/Microsoft/BashOnWindows/issues/80)

* Interix has production code for terminal-style control sequence processing in Consoles. (https://github.com/Microsoft/BashOnWindows/issues/111 https://github.com/Microsoft/BashOnWindows/issues/243 https://github.com/Microsoft/BashOnWindows/issues/27)

* Interix has the mechanism for sending signals to Win32 processes. (https://news.ycombinator.com/item?id=11415872)

* Interix had an init and could spawn daemons. It could also run POSIX programs under the SCM. (https://news.ycombinator.com/item?id=11416376 https://github.com/Microsoft/BashOnWindows/issues/229 https://github.com/Microsoft/BashOnWindows/issues/206)

* The Interix build of the Z Shell runs just fine. (https://github.com/Microsoft/BashOnWindows/issues/91)

it incompatible with its previous version, but OTOH if a Linux binary works without recompilation, is it a problem?