I'm quite interested to see how this will progress. As many other developers may have experienced, I find I have to know both VB and C# to get things done (as well as C, C++, Java, shell scripting, etc.).
Co-evolving the languages, I think, would be quite beneficial - at least to me. This would reduce, if not eliminate, my consistant need to write a library in C# because VB doesn't expose the functionality I need - and, once in a great while, the other way around - then drop the library in my project.
I'm also anxious to learn some F# in the beta version of Visual Studio 2010 I'm testing. I'm intruiged by Luca's comments about F#.
Finally, as the video addresses, it will be interesting to see if this co-evolution will result in a new language eventually.