WWI aircraft were used for other things besides shooting at each other.
Artillery spotting, reconnaissance, photo reconnaissance, depot bombing and balloon busting. There were even aircraft carriers, sea plane tenders, torpedo carrying planes that sank shipping in the channel and medditeranian. The fighter was developed to protect the bomb droppers and recon aircraft. Jousting exclusively with each other developed out of the need to protect or hunt down the recon and bomb dropping planes who had a greater day to day strategic impact on the war. For a bit more dimension to the WWI arena introduce recon and bombing aircraft. Not to bomb strat but, to try and get from point A to point B and back alive to brag about it.
Have somthing like an Aviatik, R.E.8 or Halberstadt that can fly from it's home feild to snap a photo of, or drop a small bomb on an enemy location in either of the other two countries. The photo of the target or bomb drop at the target is recorded as proof of reaching the target or point B. If the plane gets home and lands, the pilot gets a mission success message. If he gets lucky and shoots down another plane, a success message for that too. In WWI a recon pilot and bomb dropper pilot had a very short life span. They and thier gunner could put up a good fight. But fighters chewed them up much of the time. It would take the same kind of skill as landing kills in a B5N to perform one of these sorties. In WWI the paths and locations recon aircraft would fly were pretty static and well known. Thats why fighters escorted them. Could do missions to escort recon or bomb droppers to and from a location to start up furballs.
Balloon busting was very dangerous. Lots of gun emplacements and some sites had fighter patrols to support them during WWI. Have balloons with ack setup along the fronts back about a mile that regenerate in 10 to 15 min after being killed. There may be some players not up to flying straight into a WWI furball with fighters. Recon sorties and balloon busting would be other things they can do along with adding a bit of dimension to the arena. Killing a recon plane is not garunteed. They could be rather nimble and were armed.
Otherwise, just put in another Furball Lake in the DA with the WWI plane set. It will save on having to create maps and opening another arena. I'm assuming most everyone who wants a WWI plane set just wants to up their wood and cloth kites and tear into one another willy nilly. I would think without a bit of extra dimension this will get stale and have a small following. I remember the WWI arena in AW.