As others have said it would be fun for FSO to try in the future, but we have a laundry list to go over before we could run WWI in FSO. I would imagine a WWI 'Scenario' list would be even longer.
1. A WWI terrain
2. Larger WWI plane set
3. Viable targets (ground and air)
4. Through testing via Snapshots and or the AVA
Once the above 4 were satisfied then we could seriously consider an FSO in WWI, which would be fun to try IMHO.