It's interesting you should ask this question. I recently wrote an article on developing spider silk through goat milk through gene manipulation. I've been very interested in the research.
Then, recently I watched a program on the Science Channel where a doctor is doing just this... only, not with pigs, but with sheep. He has a farm and has been basically injecting sheep embryos with human stem cells and he has found that he can manipulate up to around 25-27%. The idea, of course, is the same, growing organs for humans in need.
There are some benefits and drawbacks and still a lot of unanswered questions. Is 30% human match going to be better than 100% human match? Who knows?
I think there will still be a lot of the same problems that they go through now.
The real question is, can they make it work enough? If 30% is enough of a match and they go through the same amount of risk factors and rejection rates, that's still a success, considering there will be no more waiting lists and people dying by the wayside. There will probably still be fatalities, and if they received a pig donor organ, I'm sure that will get blamed, even if it wasn't the full cause.
It's an interesting question. Kidneys can function on around 10% before they fail completely. So maybe 30% of a human organ is enough to make it work. We'll have to wait and see.