Yes the power inversion needed for that is as immense as it gets.

David and Goliath.

Apart from 5* there isn't any other European political party who would be supportive of such change, or is there? Bernie Sanders, if he had been elected woukd have been enormous help to support Corbyn as they are cut from such similar cloth, but that doesn't look like it's in the immediate offing.

The people would be behind it, if only because everything else but outright fascism has been tried. (And because the majority of Europeans are sufficiently educated in history not to want to go down that road again, Hungary, Poland and Ukraine notwithstanding.) The forces of corporate militarism are strong in the North East and East of Europe, and socioeconomic solutions to poverty and lack of development, while an improvement on the iron curtain days, are still a source of rage, envy and frustration, rendering underemployed youth easy prey for simplist right wing nationalistic forces.
Just as you and Brit predicted ten years ago.

Brussels is long overdue for a fundamental shake-up. The democratic tools are still in place but there's a big shortage of leadership material, leaving us with the likes of Macron, May, Kurz et al.

Which begs the question is the EU necessary, let alone viable in its preset form? Is it still the primary preventive measure that will stop euro states squabbling to the point of repeating the darkest side of our history?

Can we afford top-heavy centrally planned economies of this scale and if so how can we make them serve the peoples' needs rather than those of the 1% as they are presently doing?

If Corbyn could make the EU more democratically accountable he would have earned his prime ministership.

'The history of public debt is full of irony. It rarely follows our ideas of order and justice.' Thomas Piketty