I'd say that, without any PODs before the war, any of the belligerent powers could absolutely have had revolutions, with the possible exception of the US, in the late days of the war.
I've got a little timeline in the back of my mind, which I've been thinking about and considering. It's not quite fleshed out and ready for writing, but here it is.
The PoD is that a more ardent anti-war US president is elected before the war, who manages to keep the USA out the war. A second PoD/ the first butterfly is the that Raoul Villain fails to assassinate Jean Jaurés in July 1914. Jaurés wouldn't join the government, especially if Guesde does.
So, Jaurés lives and maintains an anti-war stance. He receives some support in some sections if the CGT and SFIO, but nothing too major. However, the man is very vocal and the government begins to crackdown on his activities, which breeds resentment from the rest of the left. The war drags on and casualties mount.
Jaurés, in 1917 or 1918, attempts to lead an anti-war rally in Paris, but is imprisoned for his sedition. In response, the CGT declares a general strike. At the same time, there are mutinies amongst the French soldiers. The government, panicking, begins to use very violent measures to crush the strike, which simply results in even more violence as French industry grinds to a halt. The entire situation is made worse by the US refusing to continue financing the war.
The Germans can't capitalise on this because they're in a similarly bad position. A Sailor's mutiny leads to a similar situation as otl. The end results are revolutions in France, Germany, and potentially Britain, with a higher likelihood of success. If either (or both) France and Germany fall to revolution, Belgium and Luxembourg are likely to fall too, one way or another. Sandwiched between socialist Russia and socialist Germany, Poland and the Baltics won't last long.
This isn't even going into the Austro-Hungarian Empire.
You could also do something with OTL's Swiss General Strike in 1918, or with the Easter Rising, or the Finnish Civil War, or the Romanian General Strike.
The socialists had their greatest chances of success between 1917 and the early 1920s; there were even greater opportunities at this time than during the Great Depression.