Sounds like sd_doomsday from TF2, except without the flag having to respawn before the other team can take it.
Definitely an interesting idea though. To counter the camping, the attacking team would need long-range firepower to punish the camping team, as going in to fight at close quarters risks getting bumped.
Alternatively it might put more of an emphasis on stealth and ambushing, since the attacking side would be "spotted" by the flag, so the defending side could come in undetected for a swift kill and steal the flag.
Would definitely put more of an emphasis on ship combat than the current version, as speed would not be nearly as important as being able to fight.