I think it'll take years for standard dvd to be wiped out, as there are people like me who prefer indie films over the hollywood slush blu-ray has out. Some of the obscure films i've imported from strange countries will never see the light of day on blu-ray, because the quality of some of those films will not benefit in slightest from blu-ray.
I think dvd and blu-ray will co-exist for a very very long time. Film collectors like myself will not be able to replace all of our obscure film with blu-ray, so i think it'll be like wii vs ps3. Mainstream, low-income families will stick to dvd with their sd tv's because it's affordable, will always be a better variety of films available much like the wii is the cheap gaming console of variety that can be used on normal tvs and that's affordable vs the ps3 which is suited to hd tv's and lacks the variety of titles that older gent like I prefer.
PS3 = big budget hollywood style games (style and graphics over creativity)
Blu Ray = big budget hollywood movies (style and graphics over creative independent films)
Wii = small budget indie style games (creativity over graphics and style)
DVD = small, obscure, indie films (that are creative over big-budget hollywood substanceless films)
I think the two need to exist much like we need indie film as well as big dumb hollywood films... we need both, otherwise all films would be big and dumb... VARIETY, just like Wii.