We need more two-seaters, especially French ones.
The Siemens-Schuckert was just as insignificant as the Fokker E.V/D.VIII. Too few, too late. The S-S was indeed an excellent fighter, but the war ended before they were in use in significant numbers.
In my opinion, OFF really doesn't need more late war fighters at the moment, they should be added only after the most obvious missing aircraft have been added. That means two-seaters, no matter how boring they are for fighter jockeys. Naturally I want OFF to have all the WW1 aircraft available one day, but it won't happen anytime soon and things must be prioritized. The Pfalz D.XII and the Roland D.VI would be more important additions to the late war German order of battle than any Siemens fighters. At least they saw service longer than the E.V and the S-S, the Pfalz in relatively large numbers.
I hope after P4 is ready, the devs will release aircraft packs for it. I'd be the first to buy a two-seater pack, for example.