I'd love you so much if you planned to develop the new sdk all in C#
Well basicly with mono integration anyone with enough skill in any .NET languages, heck even a kid (14/15 years old) fresh out of the 11th year (of the portuguêse school system) in programing could do that with java... you are asking for C# especially so I presume you know it well.
In my opinion I agree with the use of .NET languages, but the BASE sdk is of the Rotators choice, if i'm not mistaken every .NET language supported by mono is treated the same. So you can do one script in javascript other in Boo , another in C# , f# and so on after being compiled they are all the same...but of course its best for you to stick with one or two languages than having an application working with all .net xD