I will go out on the limb and say "plausible" even if improbable, but you have a lot of groundwork to do, the changes will be subtle and the effects potentially enormous. First I do not think you get the USSR, instead you get some far-left dominated revolutionary government. So that alone is significant. Next the alliance.
In 1915 you have a British election and the Liberals likely lose, the Conservatives will not be any more pro-German but they will likely get things rather messy trying to unravel Irish Home rule. I doubt the Anglo-French understanding lasts long without Grey and others holding to it. Russia was the up and coming power that by 1916 likely looks more menacing to the other powers, Britain especially. Even the french may come to feel too ill at ease being allied to the autocratic proto-Super Power. My understanding is that the Socialists were leaning to rapprochement with Germany. That is a long way from an alliance but you only need to plant the seeds and give it some favorable breaks over time to argue for a very different thinking in a decade or so. Let us assume that an Anglo-German naval treaty results out of a Moroccan Crisis, that the averted war with France cracks into the frosty relations and the Albanian Crisis goes far closer to the brink with the Czar playing more openly aggressive. If you dare have the assassination of FF go forward but links to Russia surface early enough that it averts war but discredits Russia. Now have the Russians seek openly round two with Japan. That puts Britain and Russia back into opposition, France is no longer poised for war and Germany is the best counter weight to the Russian juggernaut. Assuming Nicholas lives as long as Wilhelm II you have him running things to at least 1941? Give the crazy Monk some more influence, a failed palace coup against him, a failed war versus Japan or even solely versus Germany (maybe with A-H) and you have the possibility of a revolution as Russia has seen in past lost wars aftermath. And I do not think the USA is isolationist, rather it will hold to the Monroe Doctrine, turn its nose at Europe and be right in the thick of Chinese machinations. It should be a better friend for France all things considered but both Britain and Germany will command strong cultural ties too. A wacky sort of world this one.
