Although I would agree that a "victory" would do little to spur real changes, from the bits and bobs I have read it appears the internal pressure was mounting to curtail the power of the Kaiser and it appears emulate the British. I believe the democratic impulse stretches back to at least the Confederation of 1848 and the follow on Frankfurt Parliament, so I think German liberals had plenty of history to support continued enfranchisement and democratic reform since modern Germany itself looked back to this era to underpin itself apart from the "Reich(s)". Given the swiftness of revolution in 1919 and the strong political power of the Social Democrats through the Weimar period one can argue that the monarchy in Prussia was very much open to change short of what happened. Ironically it appears that Prussia was the most democratic region post-1919, it and I think Wurtemburg had the most liberal constitutions, were strongly SPD, and so on. Given no revolution and some years it is arguable that the trend would be something more like the modern monarchy, a figure head of state who serves as a uniting symbol but only paid token respect to out of history, the real power remains in the democratically elected diet. Only Bavaria might hold out longer given the popularity of the King. And from how Wilhelm moderated in his old age one might see him agreeable to this erosion so long as the trappings, pomp and flattery remain unchanged. I think it would not be until a later generation for the monarchy to fully fade though, for example an Englishman of 1920 or 1940 had a very different sense of loyalty to the Crown than the average bloke does today, they still change the Guard and publish rude comments in the paper, it is now more love/hate, a vestige of another era, I see no reason that the obviously very progressive Germans that took up power after the war would not have won much the same cultural as well as political battle. The challenge would be Communist revolution and a monarch might have been a lightning rod for revolution if the Depression still occurs.