I think it would be a nice feature to be able to do /fly at spawn and other areas around spawn like /warp crates. Since PVP is underneath spawn there might be a few concerns but it would be cool to be able to fly above the PVP area also as a spectator but soon as you reach below the spawn level and enter PVP the /fly command will be diabled forcing the player to drop down into PVP and engage in combat.