Virtual extension methods -- a strawman design

[Brian Goetz]

> A compiler only approach will not work because
> introducing a new method in an interface breaks the *binary*
> compatibility.
>
> like Neal, I am in favor of a VM only approach.

As you correctly point out, the choices are VM-only and VM+compiler, and 
compiler-only is not an option.  I see pros and cons for both options.  The 
VM+compiler option is obviously more work for us, but seems likely to reduce 
the impact on the tools ecosystem.  Ignoring the "which is more work" aspect, 
can you outline what you see as the advantages of the VM-only approach?