Does it include the source? And how liberal is the license?
MIT license
It could mean we could start adopting it and then at some point down the road they could discontinue the open version and start making closed features/updates.
Don't get me wrong, I'm very pleased that this is the direction Microsoft is taking. I am just still very skeptical.
They could do that if it was GPL, too.
With MIT or GPL or any other FOSS license, if there is a sufficiently interested party, they can, however, maintain their own version starting with any Microsoft FOSS release; Free software doesn't mean that the original owner can't release proprietary derivatives in the future, it means that what has been released Free can always be used -- and maintained -- as Free software by anyone who wants.
Of course, there is a cost to that maintenance role, and you have no guarantee that someone will take it up if the original maintainer drops it or decides to release proprietary software instead. Free software gives you the right to spend your own resources to maintain it, not the entitlement for someone else to maintain it for you indefinitely.
MIT vs. GPL is pretty much irrelevant here.
Contributors to .NET need to assign their copyright to the .NET Foundation (http://www.dotnetfoundation.org/faq), which seems impartial but also has a board of 100% Microsoft employees. If .NET were GPL, then only the .NET Foundation would have the power to let others create proprietary extensions, which I guarantee they would give Microsoft.
MS is the copyright holder so they could make proprietary updates whatever FOSS license they used, GPL v3 included.
If I remember correctly, Microsoft is making a lot of money off of Android by licensing patents.
People who have an issue with the MIT License (on the patent issue) fall into one of two categories:
a) People who've put it in the same category with BSD in their heads at some point, associating with it the same shared caveat about patents, and
b) People who understand the distinction between the two but are unsatisfied with how terse it is (especially in contrast to e.g., Apache 2.0). This isn't helped by the fact that the MIT License doesn't actually use the word "patent", and the closest it gets to saying "irrevocable" is "without restriction"/"without limitation".
In any case, Microsoft also included a custom patent grant at the time they announced the CLR's availability on GitHub and its new, more agreeable license terms. (Unfortunately it doesn't include the word "irrevocable", either.)
I know this is sounds silly, but I wonder if it's a thing or not that when a software company publicly releases some valuable code open-source, then there is always someone thinking: "better fork this as quick as possible! you never know!" :)
There are quite a few products around which fit that type of scenario - where an older, free version is still circulating while the company now distributes a close source paid version.