This is a suggestion of an upgrade to the valkyrie that separates it from a Liberator/Galaxy Wannabe. Allow the Valkyrie to have a Wraith cloaking device onboard with limited energy pool that operates like a stalker that it drains when moving. Additional levels of this increases duration/reduces recharge time. Aircraft weapons cannot be fired while cloaked (same as Stalker Infiltrator). Cloaked Valkyries can be parked and use squad logistics as a type of small aircraft Sunderer but not a whale like a Galaxy. Occupants are also cloaked. Occupants firing disrupts cloak for Valkyrie and occupants. Other ideas: Offer a nose gun sensor with TAG that can be used to mark an individual target for any nearby friendlies (AWACS-like), providing bonuses to lock on times & visibility (perhaps a HUD outline of target) This sensor package replaces the gun, making the Valkyrie a pure support craft. Pilot/Spotter get shared xp for spot/destruction of designated targets.
No... no aircraft in the game will ever have any sort of cloak. If you were around when Wraith was introduced you would know the glitch where it was possible to use on a Liberator. Although you could not fire the weapons with it active it created an insurmountable opponent, if appears and kills you, then leaves without a trace. Even though the Valkyrie does not have nearly the same damage on weapons it would increase exponentially with a cloak. As well, the Valkyrie is already damn near impossible to see when flying a ceiling height, this is abused greatly to continuously drop Light Assaults onto a battle and C4 an entire armour column. The ONLY deciding factor in that is you CAN fight the vehicle and see where they are dropping from. Remove that and this tactic would be uncontested in efficiency. The Valkyrie does need changes but never what you proposed(It has Scout Radar so your TAG idea is useless). The weapon should instead have 360 degree motion, and it could be a somewhat faster airframe. This is all the vehicle really needs to be made more viable.
Cloaking on a flying vehicle with rumble seats sounds like something that can be ultra abused. An invisible platform to drop landmines and c4? No thanks. The Valkyrie needs to be tuned so it doesn't have to rely on Engineers to resist more than 5 seconds. It needs weapons to be more in line with the other turrets on the game and the turret must be free to rotate 360°. Still the biggest problem remains Galaxy, Liberator and Esf cover every niche of the air game. Something has to be taken away from them and given to the Valkyrie. Imho that should be A2G CAS.