Honestly while I disagree with exploiting dead actors I can see why he is suggesting it. I mean I was so suprised when in T4 they used a computerized version of Arnold. That got me thinking of how many other actors could play in movies without actually doing a thing just being digitally placed in the film.
I think this would work even better with Carrey Fisher and Mark Hammel. Just get them to voice act while digital versions of them do all the acting in Episode 7,8,9!
But I think the family should have to consent and in the future actors should start including these things in their will.