Here is what I think about that. Let me start from seemingly unrelated factoids. And thus manipulate you to the conclusion.
[2016 Mar 31]
Before you jump to conclusions please consider this: By this move, Microsoft is not using Xamarin, Microsoft is giving it away. And that is the core logic here.
[2014 Nov 18]
The reason Microsoft has been able to keep both Android and iOS versions identical is thanks to a new cross-platform approach to the codebase of Office. “It has required us to be great at writing platform code for Android, code for iOS, and code for Windows,” says Atalla. All of that effort has been put together into a single platform so Microsoft can share code across iOS, Android, and Windows. The benefit is faster updates and more features for Office users. “Over the past year, we’ve had 150 different updates to Office applications across all platforms,” says Atalla. “We’re moving very very quickly in adding capability and adding functionality.”
They are talking about Xamarin here surely? Well… no. They do not talk about Xamarin.
This is description of pure C++, MSFT multi platform foundation made for next wave of Office Apps. Put this together with already brewing confusion about Xamarin vs MSFT, and you do not need a lot of spice for a very juicy gossip.
Yes here they/we/whoever are not talking common multiplatform runtime, that is true. But, I think Xamarin has lost. MSFT has decided to implement common multi-platform platform (sic) itself, vs buying Xamarin or working with Xamarin or some such long winded excersize. Microsoft solution is currently not a single monolithic executable providing a common runtime that is true. And significant. For me this means they have finally concluded that is not a best approach. Especially when needing and using native UI.
In essence now after next Office wave is shaping up publicly, it is clear MSFT does not need Xamarin. I do not think MSFT will be against Xamarin efforts, quite the contrary, but still Xamarin will not be the foundation of any MSFT made, cross platform code.
End of story? Not yet. The end of Xamarin story is detailed here. It is called “AirSpace”. The new Microsoft Cross Platform Architecture.
It is not entirely clear is this architecture implemented as a “tool chain” or a “platform”. I think this is combination of both. The “thing” spills out common modules yes, but they are compiled in different binaries for different platforms. (platforms are listed on the left).
As the UI parts are definitely different since native UI’s are used, it is even less clear (from this picture) what is this “AirSpace Frontend”. Probably some abstractions (and tools) to ease up the multi-platform UI building.
But one (key) fact is certain here: Microsoft has left common run-time architecture behind. Above is a “tool chain” and “common” platform. But for multi-platform software production. Not for providing common run-time.
In case you have not noticed, Office and other Microsoft flagship products have never been running on top of CLR. Or implemented using .NET, C# and a such.
This all, seems to me as an EOL (end of line) for Common Language Runtime too. In any case, end of story for Xamarin, foster-child.
(For the continuation of this speculation please proceed here)
[Update 2015 Feb 04]
Yet another merciless nail into the Mono coffin: Microsoft takes lid off .Net Common Language Runtime sauce