I think if other aircrafts were added the arena would be interesting.
I haven't flown WW1 sim since Red Baron and Red Baron II, even with all the bugs RB II had it was still an enjoyable game - allowing you to paint the aircrafts and add different markings as aces did.
If HTC could recreate the WW1 environment RB II had it would be quite enjoyable, however since HTC only has so much manpower to go around, I wouldn't want anything taken away from the WW2 arenas.
If he could? Few planes like nieuport 17, S.E.5.a and Albatros DIII would bring alive the arena.