A menu is not a meal. Bernie has put out a list of different potential options to fund M4A but he hasn't put out a funding plan. He hasn't committed. He himself admitted this after Liz put out her plan and he said he doesn't feel like he has to release a financing plan.
Yes, a detailed financing plan is completely superfluous at this stage. Was the wealth tax suggestion enough for you to say "this student loan forgiveness plan can work" or did you need a detailed breakdown? She had to do this because she needed to justify why she was refusing to acknowledge a middle class tax increase. Since Bernie hasn't handcuffed himself to convincing Americans that their won't be any tax increase, he has a multitude of options and according to YouGov polling, the difference in feelings about the funding mechanism doesn't even break the margin for error.
Warren’s Head Tax Is Not More Popular Than A Payroll Tax
So to be clear, this was an unnecessary step except that she needed cover next time debates roll around. It's good political strategy, not great or necessary policy strategy at this stage (and I'll repeat for a clear good faith approach on the issue check out Bruenig's work).
The gap Liz is filling here is a reality gap. Bernie damn well knows his M4A bill isn't being passed in the first week of his Presidency. At best, it's a symbolic gesture.
We both know the difference between introducing a bill and getting a bill passed week one. You're too smart to misrepresent Bernie's promise like that. Was it a shot at Warren? Yes, her single payer bill won't be introduced until three years into her term on her proposed timeline. Did he promise M4A passage in week one? Of course not. Week one is when the fight to get it passed starts is what he's saying, not in year three right after a bunch of legislators just won elections and don't have to sweat out pressure from constituents to pass the president's key legislative goal.
Meanwhile, thousands will die unnecessarily, and millions will have no healthcare. Liz's point is that she isn't waiting for the "revolution" to expand healthcare as much as possible to millions on the road to M4A.
There's a baked in assumption here that I don't particularly agree with. Whether you go with M4A or a Public Option, the Republicans and donor push back will likely be just as bad. That means you'll need a heavy amount of pressure to pass even a Public Option. Setting that up as the first benchmark just takes it off the table as the compromise position for the Manchins, Sinemas and Blue Dogs in the race. Even getting a simple majority via Budget Reconciliation is not going to be a walk in the park unless we get a really good election result. And at the point where a first hundred days Public Option is feasible, I think the path for M4A is likely a lot clearer as well.
Now, we can discuss the feasibility of passing Liz's transition plan, which can be done through reconciliation, vs passing Bernie's M4A bill, which will require a fillibuster-proof majority to vote for it, in the first 2 years of his presidency. To me, only one of those options is operating in an environment of reality.
If we're saying the government will inevitably botch healthcare expansion to the point that a public option will be disastrous and give Republicans talking points, what the hell are we fighting for M4A for?
Hang on here too. Liz's transition plan gets us to a Public Option. The M4A next step would have the face the same legislative challenges that Bernie's would. Now if you're assuming that the Public Option will be so successful that passing M4A next will be easy...Congratulations, you've endorsed Pete Buttigeig's Medicare for all who want it stance. That's not a bad thing, but let's call it what it is and personally, I don't think it works out that way.
You've now drawn a line in the sand for the Republicans at that Public Option. You've just spent however much time fighting to get it passed and you had to use legislative trickery to get it through (this is the optics, not how I view it personally). Now you are pressing an even bigger policy movement and the plan is to do it within a couple of years of that last major fight over legislation.
The reality is that even if you view a Public Option as the only feasible option to pass, you'd actually give yourself better leverage to get that passed quickly by starting the fight at M4A. It's a simple negotiation tactic and you'd also begin to introduce arguments in the affirmative for M4A out the gate instead of waiting while you pass a Public Option before going, "by the way, we know we just passed this one...but here's an even better one." You even acknowledged this in the past and in this thread responding to Harry Reid's belief that Warren would eventually pivot to a Public Option...
Both Liz and Bernie are playing the game right.
Support M4A as your starting position so you can extract the best deal possible when it comes time to actually legislate. Reid is talking too much here, peeping game and undercutting Liz's bargaining position 
, but he's ultimately right. Bernie would do the same. It'd be criminally negligent if the President didn't. The only people who seem to think M4A is going to be a reality in the immediate future are Bernie dead-enders who ascribe to him some magical ability to turn Republicans and corporate Democrats into socialists.
Thankfully Bernie is smarter than that and has shown himself to be an effective pragmatist when it comes to actually wielding power.
I 100% agree with this post. If Bernie's hands are tied, he will push through whatever the best legislation is that he can get passed. The criticism of Warren here is that she's using poor strategy by showing her hand. And even by your old standards, that isn't a necessary evil.
However, it's not just Bernie folks that don't trust her. A lot of people in the general public don't and won't trust her and with some justified reason for her consistent record of being wishy washy in both her personal and political life.
Need more of this.