generally speaking, a flag alter the technical characterize and further the tactical capabilities of a tank. We should think about what exactly alter the specific flag. Positive flags improving one specific capability. Obviously tiny makes much more easier to survive on a rouge battlefield. A lot of flags are perfectly defined and balanced. But bad flags ... I think bad flags could mostly erased. Even some good flag could could suffer a adjustment. And more team-flags are welcome. But Team affecting more than 1 tank. the only team-flag presently (beside the colored) is genocide. And one word more, bzflag is for gaming human together with another human, that involves the game is based on your sensitivity and feeling. Thats why flags that could damage the feeling for the game are not good, like alter gravity.
My suggestions:
good flags
extra bullet - a lot of player counting bullets, so 1 extra makes life easier
jump- an old stuff of mine, building restricting your driving path, so a jump flag allow to jump over on non jumping server, even on jump-enabled server to jump to the 2. stage
useless- no word
bad flags- i don't need this, i'm bad enough
team flags
poison- never kill this poison guy, or all of your team dying (is an old suggestion from spacemann spiff), maybe some disadvantages like obesity
thief -fire rate like the other tanks and same range, or only to steal the colored flag
genocide- add wide angle because if he kill all he have to see everbody
