Here is why I'm against the flag inhereting any sort of impulse from weapons fire EXCEPT for the impulse gained upon death:
In Tribes 2:
I got a rare rare chance to disc it into my own hands.
I had a far far more common and not fun situation of the flag being disced around, adding a random and frankly noncompetitive element to the game. Randomness does not make for skill. The ground flag being shot is a forced stripping of the flag from the dynamic chase which made defense so fun to me. If it can't be moved by discs though... well, that's when the chase never ends.
In theory:
A mid-air discable flag means yet another random factor. Flag tossing is already hard enough, because either player can die and it's easy to miss the flag. Plus there are player interceptions. There is no need to make something like this, that would frankly be a forced stripping of the flag from the dynamic chase which made defense so fun to me.
In Tribes 1:
A non-discable flag generally meant the defense had to defend a flag in the field as if it was on a stand. It also meant that when the flag fell from a capper, you could keep up the entire momentum of the chase because an escort picked up the flag. Running battles in Tribes one were great.
Lastly, the exception to flags gaining momentum:
In Tribes one (yet not in classic) the flag would inherit the velocity of the dead capper, including any velocity that he was given by the weapon that killed him. The flag was thankfully very heavy, so it fell with a good pace (not realistic - who cares), but nonetheless stayed WITH the chase instead of slowing to a stop before it hit the ground (which is what happens in T2), thereby stopping the chase.