JC has said he will only call a VONC if he is sure that it will succeed. To be "sure", he will need strong commitments from enough non-Labour MPs in advance (presumably public ones so they can't back out afterwards). He needs moderate Tories on board, as well as other parties.
However, JC insists that he must be made PM afterwards. And he has said he won't support a Government of National Unity led by anyone but him.
And people close to him, like John McDonnell, have said that Labour intends to pursue its manifesto once it's in power. (And by implication dare MPs to vote it down, see the new Government fail, and get Boris Johnson and no deal Brexit back.)
So with all these preconditions attached, MPs from other parties won't back a VONC. Not in sufficient numbers to get the majority that JC has said he must be sure of getting before he calls it.
The parts I've bolder are news to me.
I thought it was a very specific set of proposals which would seek to block No Deal and call a General Election ... with the point that Labour wouldn't be implementing anything from its manifesto.
So what is this guy talking about?