In this scenario, as soon as the Christmas Truce takes effect on the Western Front, the German and Allied soldiers take a good hard look at one another, and se that they are just common folk with little morale to fight. Unlike in OTL, officer threats of punishment are not able to end the truce, and the soldiers mutiny, causing the truce to turn into a complete cease-fire.
In early January 1915, German soldiers begin withdrawing from Belgium and France, despite orders from Berlin not to. The governments are dumbfounded that their armies do not want to fight, any any attempt to court marshall the protestors only encourages them. Meanwhile, similar events begin occuring on the Eastern Front (however, the Ottomans and British are unable to ceasefire due to religious differences). On January 10, London, Paris and Berlin attempt a final order to resume hostilities, but the soldiers ignore.
By January 20, 90% of the soldiers on the Western Front are in favour of peace. Meanwhile, the Russian Civil War begins much earlier than in OTL. Austria and Serbia are unable to truce, but Montenegro makes peace.
By early February, all German forces have withdrawn from Belgium and France and the Irish are rebelling. On the 15th a coup in Berlin topples the Kaiser, and the new leader offers peace. On February 17th, France and Germany make peace: Germany agrees to hand Alsace-Lorraine over and pay the modern equivalent of $1 billion in reparations. France now drops out, but Britain remains in the war. On the 19th Germany pays some reparations to Belgium, who drops out. Britain and Germany make peace on the 21st with colonial concessions from Germany, followed by Japan and Germany on the 23rd with Germany ceding the Caroline Islands. (Britiain is still at war with the Ottomans.)
The Bolsheviks seize Moscow on the 25th, and make peace with the Central Powers on the 26th ceding Kars to the Ottomans. The Poles attempt to rebel, but with their potential allies' soldiers tired of war, they are put down.
In March, the Ottomans cede southern Mesopotamia to Britain in exchange for peace. Meanwhile, Germany and Serbia meake peace, leaving Austria-Hungary and Serbia as the only nations still fighting. The war continues until May 1915, when ethnic riots force the Austro-Hungarians to consider peace. A-H cedes Bosnia and Herzgovina to Serbia, and with that, WWI ends much earlier than in OTL. Only 4 million are dead, and the influenze epicdemic and Great Depression are butterflied away. Meanwhile, the Poles and Finns are rebelling.
How do you think this world will proceed?