I doubt Britain would get involved in this war, Germany and AH will be battling it out with Russia and France will sit there twiddling it's thumbs trying not to get invaded. Britain won't have an excuse to join because the CP will be tied up in the east.
There's so many factors that make it far too unlikely for Germany to ignore France (or vice-versa).
Quite the contrary, a distracted Germany may well make France
more liable to go to war. It's not at all a hard-sell to the French government: Germany's troops are distracted fighting for their lives against the Slavic hordes, how hard can it be to waltz into the Alsace-Lorraine and make good on the loss in the Franco-Prussian War? France was not bound by any great loyalty to Russia, a nation it had gone to war with not much less than fifty years earlier, it was fear of Germany that motivated the French partnership with Russia, and if you get down to it, there's not many ways France cannot get involved: if Germany gives Russia a thrashing, the French would have to join the war for fear of having their greatest asset against Germany overwhelmed, if Russia was winning, no sitting French government could reasonably be expected to sit idly by while the Germans were in the east and not in the Alsace-Lorraine.
The Germans were not stupid, and wouldn't want to hand the French so golden an opportunity. The absolute smartest decision they ever made in WWI was assuring that the Western Front was not going to be fought on German soil, whoever "gets" the war so to speak is the one that's going to take it the hardest, regardless of whether or not they win. France and Belgium had most of it fought on their soil, and they both won. France did so at the cost of roughly one-third of all men of draft age in the country, Belgium suffered similar deprivations, but these deprivations, like most of Belgian history, are forgotten by all except the Belgians.
Neither of them got a glorious, inexpensive victory by any stretch.
The hope, the absolute hope and desire of the Germans was to absolutely assure they would not be caught fighting a deadly two-front war. The two-front war they had hoped to avoid occurred
precisely because of a mistaken belief that they could easily blow one side or the other out of the war and then refocus their resources to deliver a smashing blow to the remaining side. Great powers involved in regional conflicts don't tend to stay regional, they draw in other great powers. To have that be different would require drastic alterations to the balance of power in Europe that would make the early 20th century utterly unrecognizable.
As for Britain, splendid isolation was more a splendid facade, Britain's status as an island did not make it any less of a crucial part of the European balance of power. It relied upon its strategic friendship with France and other colonial powers to keep the peace in its empire. It relied upon a large, and uninterrupted trade with the European continent. The workhorse of British dominance was its economy just as much as its navy. Not to mention the fact that Britain could not allow the formation of a continental hegemony.
Any threat to either its trade or the balance of power on the continent pretty much meant Britain had to be involved.
