The problem is that this OP requires something that would not be the case. Austria-Hungary in particular is not likely to last out of the 1910s without either 1) reverting to a proto-totalitarian system purely dominated by Germans, or 2) disintegrating in a process of attempting to contain a new round of Magyar threats in the next Ausgleich and starting WWI in this sense. Russia likewise is not going to do very well, though the Ottomans may well make it by virtue of the oil factor. Russia's problem is that when push comes to shove, Nicholas II will never seriously concede anything in any way, in any form, or in any fashion.
So this OP is asking for something that's very unlikely.
I have to take serious issue with this. AH without some sort of external pressure is very likely to just abide and coast on to the 1940's. Nevertheless 1917 is going to be a big change year if Franz Ferdinand is crowned. The Hungarians are dropping out of power very quickly one way or another. The plans developed by the AH army were fully ready to decapitate the Hungarian government very quickly, more quickly than the Honved could react. The issue would be settled before an external power could intervene, speaking of which:
-Serbia in 1914 got a new government that was dedicated to repairing the relationship with AH and wanted to rein in the Black Hand.
-Russia won't start of war over internal AH matters at this early of a date, as France would not support them.
-Romania is likely to have defected to the Russian side by this point, but won't act without a Russian declaration of war
-Italy is still in the triple alliance and won't risk become such a massive international pariah by attacking AH.
FF is going to implement universal male suffrage in Hungary and will have to do it in Austria within a few years (Austria had universal suffrage, but it was weighted to give 90% of the population 20% of the seats in the Reichsrat). This is likely unlock the floodgates of army expansion and public works projects which had been blocked for years by the Hungarians and Franz Josef's ministers. It will also preclude FF from becoming the autocrat he wants to be, especially as class conflict supersedes some of the ethnic issues in Austria starting in the 1920's. There will be major political issues to be sure, but AH is just too likely to survive it than not because of inertia and the German alliance, not to mention the Russians becoming increasingly unstable themselves and not being able or wanting to start a European war.
So if Europe somehow made it to 1939 with the 1914 powers intact (though not necessarily the 1914 power blocks) what sort of Tech would they be fighting the war with, what alliances would have endured, what sort of form would the war take, ect. I realize this is a wide open question, so speculate away.
That said I'd expect the basic sciences to be more advanced with applied science/gadgets being a mixed bag. With a generation of young men not slaughtered they would in turn become scientists, engineers, and business men all focused on the science race, which pretty much was an international competition for the European powers at the time. On the balance airplanes are likely to be somewhat retarded, but not by much. Its application as a military weapon is obvious and as more money pours into it, the progress is likely to be somewhat similar in the long run, obviously minus the burst of advances in 1914-1918.
The naval race is over in 1912 and Germany in heavily investing in her army, because her leadership realizes that by 1916 the Schlieffen plan is no long a valid plan and her army is the only counter she has to the Russian hordes now running on Russia's upgraded rail system. This means major investments in air and land technologies. France will try and keep up with this spending and was quiet an innovator in technologies at this time, especially military technology to keep up with Germany's growing population. Russia is too going to start to develop, but will be majorly hampered by public unrest. I think they'll be lagging behind, but still competitive due to their vast size and growing economy, not to mention investments by France and Germany in her manufacturing.
AH is in for a boom, because she had avoided public investment in industry and public works for years due to conservative economic cliques in the finance ministry. With the Hungarian issue taken care of and FF needing something to distract from ethnic tensions, and not being very spending adverse, he has a whole host of public works projects planned and waiting for money to fund them. Not to mention the need the army has to keep up with the growing threats surrounding her. Germany was also Austria's biggest investor, so expect that spigot to continue to water the Austrian economic garden.
Austria has huge investment potential for her agricultural sector, as she as oil fields, trade deals with Romania, and a growing automotive sector. That means tractors. Tractors mean fewer people needed for AH's massive farming sector, so lots of human capital for use elsewhere. And tanks. An Austrian colonel was the first to design an AFV with catapillar treads, so perhaps as time goes on the Austrians put out the first tank.
The trend was for fire and maneuver for all armies, so as the old timers retire, all powers are going to motorize, spread out, and firepower up. This means automatic rifles, SP artillery, AFVs though probably mostly light and medium tanks and probably tankettes, and lots of maneuver doctrine. The trend was in the direction of 1939 style armies anyway in 1914, so I think that a more unwieldy version of the OTL 1939 army exists in TTL. The air forces are going to come anyway, though will also be unwieldy. I still expect strategic bombers, CAS, and tactical/operational bombers too. The organization and doctrine will be faulty, but still there.
Radios and the like are going to give these armies the ability to operate like a modern army, so don't expect massed infantry formations.
In fact I expect every army to have a blitzkrieg-style to it. Offensive a-outrance is definitely a blitzkrieg style, but with 1939 weapons and communications expect it to be more effective.
The French are going to be a tougher foe than in 1914, the Russians who knows, the Germans are going to be quite nasty, the Brits may not even participate, and the AHs are a wildcard. They have the potential to be quite powerful, but might be weak in the end. They are surrounded by Italy, Serbia, Romania, and Russia, who will all be foes, but fortified passes block two of those powers, probably Russia too with the Carpathians in a pinch, and Serbia is highly isolated and very vulnerable to an AH with a motorized and mechanized army backed up by an air force.
