I hope you know that I am talking about support and not eliminating the other side.
I get that you are not talking about elimination of other preferences. I believe that it's your and my commitment to options for a variety of playstyles that has enabled us to have as many civil and productive conversations as we've had.
I just want to clarify that the reason I emphasized that both allowance and support of what came before must be present is because I've seen allowance exist without support (I mentioned a couple examples of this), and allowance without support is frequently treated as if the allowance itself isn't possible (I recall at least one instance where a very pro-4e poster on the WotC forums attempted to argue that a daily-only class being introduced to 4e was for all intents and purposes impossible).
I get frustrated when they leave very low hanging fruit on the table like a warlord class but they insist on jamming up the fighter. I don't think 4e people are going to be terribly upset if one subclass of fighter and rogue is clean of DS mechanics and martial healing. If they have their own subclasses all will be good.
I would also fully embrace teaching all the ways you can play D&D and I'd have playstyle sections in the DMG written by proponents of those styles. Hey I'd even let Iserith's playstyle be presented.
I get frustrated by the low-hanging fruit too, recall how certain I was that a slow-healing module would be in the pdf.
Side rant: I get frustrated by people a LOT. I'm a hopeful person at heart, and I've seen what we can be: the intelligence of Einstein and Hawking, the charity and compassion of Pope Francis and Mother Theresa, the righteous dignity of MLK and Nelson Mandela. Unfortunately, I also see what we are. It's given me a love-hate relationship with people in general, and it's probably at least partly responsible for my frequent bouts of depression (and my periodic contemplation of the sometimes seemingly inevitable ultimate relief of said depression).
True. I totally agree with you. I never liked multiclassing post 2e. I think the 2e model where you choose your classes in advance and level them all up evenly is the best approach. I'll write you a good houserule once all the rules are out if you like. I think I can come up with something pretty good.
I don't really know how much in the way of rules that you need. If you treat it like 2e multiclassing, then you just have all the profs of both (or all three) of your classes and all the appropriate abilities given your level. If you treat it that way, you really only need a rule for determining your HPs, and a rule for altering the xp budgets for encounters. I might start the attempt at xp budget rules by saying that an MC character is worth 1.5 characters (they have more abilities, but they only have so much action economy to use them with).
I think they failed to provide a game for all editions. I don't think the 4e people should be happy with 5e. I mean the true believers. Obviously many people just go with the flow and play the latest edition of D&D. That group is non-trivial in size is my guess.
For me, I think it's still to early to tell if they succeeded or not. It depends not just on the modules that are presented in the DMG but also on how good the advice and tools for hacking the game are. I said to another poster on the WotC forums that modules for what I want would be excellent, but tools that enable me to make the modules that I want could be just as good or better (depending on execution).