Hopefully 4 will have zero G enviroments were you get to float around use your thruster pack thingy. But yeah, just because he didn't have a jetpack in 3 doesn't mean he can't have a jetpack in 4. Its like saying after Reach the covenant decided to just stop producing the needle rifles and every single Skirmisher died. Its called retconing and we've seen it done before in Halo; including masterchiefs armor from 2 to 3. As long as they don't go crazy with it, and have Master Chief's armor have wrist mounted gattling lasers or something silly like that, I don't have a problem with it.
Still need scissors! Official Ambassador of Gris as of 11/26/05