I get that this is inconvenient for users on other platforms that don't or can't license it easily, the same way GIF and MP3 and similar file formats have been in the past. I don't know why the SDA picked a proprietary filesystem.
Regardless, that was something the SDA did, and they did it in 2009. How does it relate to talking about how Microsoft currently produces apps and publishes APIs for other platforms?
But even assuming that Microsoft had nothing to do with exFAT being adopted as the SDXC filesystem (yeah, right) it still relates as MS could have released the exFAT specification and they could have released the filesystem from licensing.
That would have been sign of them being a more open company, allowing integration with other OSs, but instead it just looks like since they failed to kill off OSS, they're now trying to own it. Same old Microsoft.
As for Open Sourcing .Net, what good has come of it as of today? It looks like a move to push their own environment more than anything else. But I'll tell you what: if in 2020 the decisions Microsoft are making today prove to be for the good, then I might start think better of them. At the moment, though, they've got a lot of past to make up for.
The new standard for high capacity SD Cards - SDXC - specifies a filesystem in the standard. That filesystem is exFAT, a proprietary, patent-encumbered filesystem from Microsoft.
Microsoft like to make out that they're an all new and open company, but they were a nasty company in the past, and they're a nasty company now.