The strategic business value of supporting or not supporting dynamic languages is the only relevant question. It's not like dynamic languages are endagered species that need and deserve special protection but it might be a good idea to support them; it all
comes down to whether it helps Microsoft or not.
I'd rather they support one well, rather than two poorly. Can only hope that's what's happing (vested interest in IronPython surviving).
At least as C# and VB now use the DLR for their Late binding/dynamic dispatch it's furture must be quite stable, one would hope.