Yes, that thought had occurred to me too...
I think the minimum for it to be really fun in the planned form would be something like 4 players per team - and 8 players online at the same time is actually quite a lot (I guess I'd need to organize some scheduled testing sessions to try and get everyone online together).
However, there could be alternative gameplay modes which would be playable even 1 on 1. For example, a pure dogfighting mode with no tanks (exactly like the original Sopwith), a mode with just the tanks and no planes (basically a Scorched Earth clone), or a mode with AI-controlled tanks and player-controlled planes (similar to Armor Alley). We'll see...
The level editor is now completely done, so that's good I need to go back and finish all the tank-related stuff next. I was working on a parallax scrolling effect, but I don't really like it so I'm scrapping that.
btw: I'm very much looking forward to Dungeon Dashers - I've been watching it for a while and it looks awesome. And plus roguelikes are always fun