Interesting hypothetical scenario. It raises all sorts of questions, both from a point of view of weapons technology and politics.
Assuming that WWI had lasted for another 20 years (meaning, I assume, 20 more years after 1918, which brings us to 1938, one year short of the starting date of WWII), weapons technology would certainly have progressed further and faster (though not necessarily in the same directions) than it did historically. To quote one example as an illustration, just look at the classes of battleships and battlecruisers that many WWI combatants had planned or were actually building at the time the war ended in 1918, but which were then abandoned. The British, for instance, were planning a class of battleships armed with 18-inch guns that would probably have entered service in the early 1920s; in the real world, it was only in the early 1940s that an 18-inch gun battleship class (the Yamatos) entered service. Many of the weapons that achieved maturity in WWII existed in WWI, albeit at the infancy stage – notably tanks and aircraft carriers. The same was true of certain tactics: had the war lasted until 1919, there were plans on the Allied side to mount attacks by massed tanks working in close coordination with motorized infantry and aircraft support…essentially an early version of Blitzkrieg.
However, even though I can see some WWII-type weapons being used on the WWI game board under such a scenario, the part I think is problematic is the political element: the idea that the same 8 powers who are the contestants in the A&A 1914 game could still all be in existence, and still fighting each other, in 1938. Remember, after all, that three of those states – Tsarist Russia, the Austro-Hungarian Empire and the Ottoman Empire – were already politically and/or economically unstable in 1914. Russia had already seen one revolution against the Romavov dynasty in 1906, and this had done nothing to persuade Nicolas II to liberalize his regime. The Austro-Hungarian Empire was a mish-mash of restless ethnic groups led by an elderly ruler who, like Nicolas II, believed in absolute monarchy. The Ottoman Empire had been in decline for a long time, and its leaders were both divided and paralyzed by indecision. Frankly, I’m surprised that Russia managed to last till 1917 and the other two until 1918, so I don’t see any of those regimes surviving a further two decades of war.
I said another 20 years was highly improbable for the very reason of political (as well as economic) instability. I highly doubt the war could have gone on for twenty more years without several nations collapsing from the strain.
But as you correctly pointed out, technology would have advanced much faster had the war continued. I know for example that Thompson sub-machine guns were developed during WW1, but never saw action, and that they would later be used in WW2. So let’s say the war only goes on for another 2 or 3 years. This would bring many weapons used in WW2 into the conflict.
Now that we have a somewhat alternate-historical basis, can we design rules for allowing WW2 era A&A units such as TcB, StrB, MechInf, and CVs? As I’ve said, I haven’t actually played 1914, but I know there’s a rule for when tanks can actually be built, could a similar rule be implemented for other units? I plan to buy 1914 and try it out.