I'm not as convinced as Professor Carty that it would be the death knell for national political parties. I don't see Canada being as riven by what political scientists call cleavages, as, say, Belgium is. The model proposed by the law reform commission would have a built-in kind of threshold. You'd need, probably, at least 10% of votes in a region to get one of those list seats.
To me, the worry that there would be a proliferation of fringe or extremist parties and that the national parties would fall apart seems exaggerated. I just don't see—and I share, actually, your views so eloquently stated in the preamble to the question—that we grew up or lived through the near death of the country, all under first past the post. I don't think that a mixed member proportional system would exacerbate regionalism. I don't think it would be any worse than it is now.