Social democracy has an inherently limited shelf life because you cannot stably have workers with the right to politically associate, full employment, and continued capitalist relations of production; without the disciplining of the state or of the market they’ll bid up wages until profits are gone, at which point capitalists can (in principle) assent to their obsolescence or (as in all historical cases) seize a horn of the dilemma. It’s sociopathic neoliberalism or psychopathic national/state/authoritarian/whatever capitalism from here on out until one physically annihilates us.
Or, theoretically, Some Fourth Way Out.
The various Fully-Automated Luxury models – which burn from a kindling of “such overwhelming moral suasion & inherent niceness that the capitalists find it easiest to accept obsolescence rather than fight” – are my favorites.
(Not that this is really a strike against your theoretical model, as such. Just…making a note of what victory conditions are likely to look like.)