... I would, however, question the word "substratum." I think it could
> well be an ADSTRATUM or even superstratum, considering the amount of
> non-Uralic words...
For those who question the likelihood of such a merger of two
dissimilar languages, look no further than the Anatolian group!
Hittite's the most Indo-European of the group, and that says a good
deal considering all the borrowings from Hattic it's got! Luvian and
its descendands are far more agglutinative, and use many more
non-Indo-European borrowings. One begins to wonder what percentage of
the words are Indo-European.
This kind of merger seems to describe PIE as we know it quite well;
its grammar is closer to Uralic than to the Northwest Caucasian
languages, but many of its words seem more Caucasian in flavour.
Considering that grammar is the most conservative part of a language,
this should speak for an Indo-Euro-Uralic affinity.