[gnufreex]

>1. There is stuff covered by the ECMA/ISO standards. This is covered by the Microsoft Community Promise, which is legally binding. This stuff is safe from Microsoft.

And that is only thing that is remotely safe. All other is murky. But unfortunately, even that can be unsafe if Microsoft sell patents to CPTN (like they did with Novell patents) and let them sue even for ECMA parts.

Moreover, ECMA parts are unusable on their own. Eevery single mono app also depends on non-ECMA parts and Mono is always shipped with non-ECMA parts: http://www.the-source.com/2010/12/on-mono-packaging/

As for Estoppel, they didn't promise anything for non-ECMA. It doesn't work the way you think it works. In fact, they even promised to sue:

"If someone implemented a product that conforms to the specification, we believe we have a patent or one pending that’s essential to implementing the specification."

or

"The .NET framework contains the latest developer platform for the future, and it must be licensed like Windows. Subsets have gone about as far as they should go in the standards bodies, but we need a compact subset for phones and TVs. It was noted that we have to be careful because once the horses are out, they are out forever. At the right royalty, we can have discussions around technology beyond this."