A bit of a necro here, which is sort of appropriate to the topic anyway, as the issue has made the news again.
I think that a key point was made by Professor Chris Rudge, who is as qualified to speak on the subject as anyone and far more so than most people.
I said the same thing about the results of removing the need for consent(*), but his words should carry more weight than mine on the subject.
Should...but probably won't because the decision has little or nothing to do with transplants. It's mainly about image, about being portrayed as doing something good even if it's useless or harmful or about feeling righteous. Anyone who bothers to spare a minute finding information and thinking would know that at best it might result in a tiny increase - most eligible people are already registered donors, most if not all of the rest would opt out, some people who are currently registered would opt out on principle and on top of all that only a tiny proportion of people who die do so in a way and at a time that makes it possible to use their corpse for spare parts. But it's much more popular to mindlessly emote and bask in your own righteousness, so it's politically astute for politicians to pander to that to improve their image.
* Although I would not consider it very good even if there was any reason to think it would increase the number of transplants done. A tolerable trade-off, maybe, but definitely not very good.