Look, I'd love for that to be true, but it just isn't. Biden will win by being a boring centrist, because that's who he is and that's who will win a general election (generally speaking).
With the GOP going completely off the rails the easiest path to victory is to simply go middle of the road and pick up all those independents/centrists and conservatives with brains. Progressives will vote Biden regardless because Trump (or any Trump wannabe) is too terrifying of a reality.
This country has never shown it has some giant progressive silent majority - Bernie would know, he bet and lost on that materializing in his own presidential runs.
I don't see Democrats running hard on progressive policies until either the GOP starts running moderates again (forcing Democrats to pickup votes elsewhere) or young people prove they can be a force at the ballot box.
All this is not to shit on what Biden has achieved, because he has done things for progressives, but I don't see him suddenly switching to anything resembling a "strong progressive agenda" because it will just give his GOP opponent ammo to claim "see he's radical too". Biden will be the most boring, normal politician he can, while highlighting how bad things will get if his extreme opponent gets into office, and that's probably the smartest thing to do.