I think we need to have one Indian origin keynote who understand ground problems and his keynote will big boost for our audience , that was the whole reason we started with Indian origin Keynote speaker concept 2 years back.
IMO, to understand ground problems, you have to be based in India. Someone who left long ago can't be expected to know what the current ground situation is.
I'll agree with Noufal that the sensible way to define the criteria is that this person must be based here.