Alternately, and this might both bold and a bit out there as far as ideas go, have Austria-Hungary make a seperate peace. IOTL, they tried negotiating their way out of the war in early 1917. Nothing came of it. The French published the letter, causing a major embarrassment for the Emperor and the Germans to tighten their leash on Austria.
But, suppose Central Powers performance is a bit better and the Entente position a bit worse ... not enough to really change the outcome of the war, but make the Entente harder pressed and facing a tougher fight. So, the Entente decides that giving Russia some relief, weakening Germany and cutting the flow of supplies between Germany and the Ottomans justifies giving Austria a peace treaty. Maybe it's a white peace, maybe there's some minor border adjustments and reparations to Serbia/Russia, whoever, but Austria goes out of the war.
The war continues and ends with a German surrender, after another year and a half of bloody fighting that leaves Germany, Russia and France hollow ruins. Russia might even avoid the revolution. Italy is obviously pissed, but all of Austria's other rivals are neutered for the time being.
This buys time for Austria to reform. The national councils are effectively powerless, so internal forces, which still call for autonomy (rather than independence). Though the success of the reforms is up in the air, they might succeed - certainly, there was enough revolutionary belief among the populace to force Vienna'a hand into making real concessions.
So, best-case scenario: Austria-Hungary bows out of the war early, survives and everyone else is ruined by the war.
There's likely an Austro-Italian war ready in a decade or two ... Germany is certainly going to want rev
This seems to be poor for them as their enemies will rearm in time and be back for round 2 and now they have no allies to back them up. Plus Romania wants land from them still, combined with a rearmed Russia and Italy that wants land as well and this time Germany not helping them out, well long term their position is poor.
I think best case scenario, is not an early victory. Instead some of the deadweight has heart attacks/strokes or sidelined. However AH executes war plan Russia and performs better avoiding the pounding they took OTL. Ottomans also do better vs the Russians to keep more pressure on them and so they have to keep reinforcing that front. Let the war continue to grind on in the West as that weakens Germany somewhat post war but the war in the East is going the CP way.
With success in the East in 1914 the CP decide to focus forces that way in 1915 to try and drive Russia out of the war and push far into Russia, Bulgaria joins in against Serbia which has exhausted itself launching attacks against prepared defenses. AH is doing well so Italy stays neutral. Russia is doing worse so maybe Romania jumps in mid 1915 when AH, German and Ottoman forces are pushing back Russian armies.
Russia is a mess at this point and trading space for time, AH is in better shape not needing to recruit as many men since no Italian front and fewer losses on the Russian and Serbian fronts. So more men hone working the fields, mines and factories.
Germany is still bleeding on the Western front where I can see the UK and France are throwing more and more men into the grinder to relieve pressure on Russia so all three countries are getting worn down.
Now 1916 happens, Russia is very obviously on the ropes and let's say they actually lost several armies during 1914 and 1915 to encirclement, casualties, and desertion. Now with German, AH, Romanian and Ottoman troops pushing deep into Russian territory and the Russians scraping the bottom of the barrel revolution comes a year early, probably late 1916 after a failed counter offensive fizzles and they get pushed even further back. At this point Russia places out in early 1917 with lots of reparations and loss of territory along with puppets.
Now AH can partially stand down some of their forces while Germans send forces west and with no USW and no USA entrance funding runs low for UK and France so they have to do with reduced supplies dwindinling to almost none from the US. With the threat of veteran troops arriving and a worsening supply situation UK and France try for one last offensive which fails and eventually sue for peace.
AH is getting reperpations from Russia and also some puppets. In addition they suffered fewer losses and so did not need to call up as many men, more so with Russia taking worse losses and Ottomans doing better so contributing more against Russia drawing off forces plus Romanian armies also fighting and drawing off even more Russian forces.
Germany wins but has still suffered a higher loss rate and had to canablize themselves to an extent to keep producing war material. This means for a time the gap between them and the AH will be smaller then pre war.
With this victory an economic block arises of the CP, however with a weakened Germany and stronger AH, Ottoman, Bulgaria and Romania, Germany cannot dominate the block and AH will have a strong position inside of it.