Oh no! wumpus will be sad.
That seems highly unlikely. I don't think dropping something would even mean anything - the more important point is to find coherent messages and perhaps add platform pieces that will play well. Some things are negotiable, but climate change, gay rights, and generally fighting for the underprivileged are the core ideals. I think the big problem is that the "tax the rich" messaging isn't resonating all that broadly and is already entrenched in ways that make it more a difficult policy position. They should instead go after specifics: create a whole series of pigouvian taxes on ways to spend money that drive up costs for everyone else, like spending too much money on college, health insurance, rent/home purchases, and perhaps a few other targeted things like gas or power consumption. If the tax is only on people who spend more than some high threshold on these things, it will hit only the rich, and it can be used to subsidize these costs for the poorest - tax overpriced colleges or private schools to send more people to average colleges and increase funding of public schools, tax cadillac health plans to pay for basic ones, etc. It's taxes, and surely someone will be like, "My opponent wants to put a tax on education!" It has the advantage, though, of being a fresher idea that doesn't already have ingrained memes and the accompanying eyerolls.
Really, though, the best idea is to go into rebuilding mode. Cultivate talent, lay low and try to work with the GOP unless they cross one of the hot-button lines, and try to rebuild enough to take back State legislatures by 2020.
I think this is more propaganda than reality. I know a lot of liberals and most of them are not at all dismissive of other viewpoints, only of disregard for facts. I've only ever heard the term "flyover country" from someone trying to get liberals to listen to conservatives, the backwards cousin-fuckers stereotype is perhaps more acceptable than it should be, but I've never heard it used to dismiss a policy discussion, and I've certainly never heard anyone hope big swaths of the country would die so we could enact some laws.
I agree that breaking ties with banking would be helpful, but bankers are important to the country and the industry isn't going away, so someone has to be their advocates. I'm happy for Democrats to cede that to the GOP, but that's kind of already where they were, policy-wise? I mean, Clinton's platform was pretty strongly anti-Wall Street and the remnants of the party are even more so. If people were swayed by the fact that Clinton got paid to speak to bankers, then they are again simply allowing propaganda to dictate their opinion. Trump is considering Jamie fucking Dimon as Treasury Secretary, so I'm thinking the Wall Street hate was pretty manufactured.
I will say, though, that the Basket of Deplorables comment, which seemed like a good way to call out Trump's really shady backers, probably cost her the election because the phrasing played directly into the worst possible perception of her in the Rust belt (that she thinks everyone outside the coastal elite is a racist hick). If she had said that Trump was being propped up by a fringe group that she likes to refer to that way it would have been a much cleaner hit.