Biden has it in the bag now. Decent wins for him in Arizona (which as a western state with a large hispanic pop was in the category of states Sanders has been stronger in), Illinois, and a really thumping win in Florida.
Regarding narrative and expectation: I think one should take platforms more seriously and literally than almost everyone does. If one analyses it, most politicians attempt most of their platform, most of the time: we just have a strong selectivity bias for remembering the calls they made which went against their platform. Conversely I think people's past makes slightly less difference than people expect, because politicians operate in the environment they're in, and are aware of who they're beholden to and who they need to keep on-side and what they can't get past their own party and so on. Of course that's not to say it makes zero difference, but I think it makes less than people expect.
I don't think for example that healthcare is a terribly hot-button issue for Joe Biden. But I suspect that a public option for medicare is something everyone will associate him with heavily by November, because he can't afford to not make that a key part of his plan - in the current situation, health topics will be paramount in people's minds, he's got to show some incremental progress at least in order to appease the Sanders wing of the party - and then in office, he's overwhelmingly likely to attempt to follow through on that, because the expectation has been set and that's the milleu we're in.
Looking ahead to the general, the 538 engine hasn't fired up yet, but the RCP poll averages give a rougher idea of where we stand - and they generally look OK but not stellar for Biden. He's a modest favourite in enough states to win, but Trump seems to be polling alright in Wisconsin and Florida in particular, which basically implies he's still competitive both in the midwest and the sunbelt. On the other hand, Biden seems to be a modest favourite in Pennsylvania, Michigan, North Carolina, and Arizona, which would see him comfortably over the line. Interestingly the few polls we've had out of Ohio have been really pretty bad for Trump too - it's very hard to see how Trump wins without keeping hold of OH. I think Trump's best case is that he holds on, just about, and Trump's worse case is a blowout loss, with the likelihood/midpoint guess being a narrow Biden win with some ground regained in the midwest (maybe MI and PA but not WI and OH), plus picking up North Carolina and Arizona or something in the south to get him over the line. We'll see.