Possibly, but lock-on AA rockets from the rumble seats might mean it never has to engage any closer than 100m. Guided AA (or AT) with an unobstructed line-of-sight = good. Even unguided rockets might be great. I wonder if they'll be set up as left/right doorgunner seats? I can imagine the hilarious "flippity-doo-dah" manoeuvres pilots will be pulling to keep up a steady stream of rockets firing from their heavies as reloads happen on either side. Just need to work out a way of sticking an ammo pack on the thing. But you could also just re-ammo your heavies and repair on the ground, removing the need to ever fly back to an airpad. Or establish mobile airfields.
Some of the funnier things that might come up with the Valkyrie.
C-4'ing or sticky-grenading things whilst in flight.
A2A firework wars. Or with flashlights for the ultimate in pointlessness.
Concussion or smoke grenade ground suppression runs (or Vanu Mobile Disco Party Smoke Machines as they'll come to be known).
Air-knifing.
Regenerating Air-Tank. Constantly repair the valk with 2 engies in the rumble seats. Like the harasser variant, but twice as broken and flies.
A2A repairs of other aircraft.
LA sky ballet with twelve valks providing jump platforms for them to air-dance from. Or do slightly more useful things.
Also, the vague possibility of mid-air seat swaps so your pilot and turret gunner can unload their rockets once the rumble seat heavies are empty. "Honestly, just jump out, we'll swap places. I'll catch you, honestly. Everyone jump on 3, 2, 1, SWAP!"
Also: Engy turret updates. Oooohhhhhhh. That might be very cool.