As must be obvious, I think now that the spread of Indo-European languages had some demographic impact. It wasn’t analogous to the spread of English to Jamaica, or the existence of French as an official language in Congo-Brazzaville. Because of this, I now believe it is possible in the near future that scientists will reconstruct the genome of the original Indo-Europeans. How?
1) Find the intersection of genetic segments on the chromosomal level which share identity-by-descent between widely separated Indo-European groups. For example, Greeks, Swedes, and Punjabis.
2) Check to see which of these intersecting elements is not found in nearby non-Indo-European groups. For example, Basques, Finns, and non-Brahmin South Indian Dravidian speakers. At least to an appreciable frequency.
My current supposition is that proportionally this component won’t be preponderant in most places, but, it will be significant. By reconstructing an Indo-European genome we may actually have the ability to ascertain the population’s urheimat, as we can compare its genetic distance to extant populations.