Doesn't appeal to me.
I like all my movies in one place on my iDevices. I also like to own movies outright. It doesn't happen so often now but in the past it was known for movies to be banned from sale after release. I assume that if this happened today then the ultraviolet copy would be unplayable.
For the sake of about £7, I'll download a proper copy from iTunes if I like the blu ray.
The same could happen with films from iTunes though. Apple could pull them from the iTunes Store, preventing them from being re-downloaded (or streamed). Hell, it could probably even revoke the DRM permission so you can't play them anymore too even if you already have them. You don't own the film outright - you have a licence to watch it.
[Not saying it's a good thing, just pointing out that in this respect iTunes is no different to UV]