Ryan has promised that no one will be worse off after Republicans replace Obamacare. But the only reason they are talking about delaying replacing Obamacare for two or three years or more is because even after talking about it for five plus years, they have no idea what to replace it with. They appear to want to go back to the pre-Obamacare status quo. But they don't think that is politically viable.
Just like you can't jump off a building with no plan on where you're going to land (not if you want a good outcome), "repeal and delay" is a farce which is being gobbled up by the Washington press corps like no one's business. Sad! as Donald Trump would say. It makes zero sense except as a plan to put off the blame for the human carnage until after Ryan has bagged his tax cut.
Let's repeat this again, there is zero reason to wait a day to replace Obamacare with whatever Republicans want to replace it with — no policy or legislative logic whatsoever. The only logic is kicking the can down the road, because after five years Republicans have no idea how to accomplish what Obamacare accomplishes. So they have no replacement. What they do know is that by repealing Obamacare they can lock in a huge tax cut for the wealthiest Americans. So as if you're one of those 20 or 30 million Americans about to lose their coverage. All is not lost, Ryan got his top supporters a really big tax cut in exchange for the coverage you got under Obamacare.