At this point we are not totally sure how CAS is going to work but its most likely going to be just dumb bombs because there wasn't many guided weapons back then and the ones that where around where not used very often, epically when it came to CAS.
But even so I wouldn't have that stop you from putting jets on your map, but I wouldn't exactly have infantry "rely" on anything as I believe that's a bad move to make a player rely on something. Its better to say that if you use this asset (ie, in this case CAS) to the best of your ability you have a much stronger advantage than you would if you where just fighting without them, but it isn't necessarily necessary for your team to win the battle, much like how the Cobra is on Muttrah, you can still win the battle without the Cobra, but its much harder to do so and with good CAS support from the Cobra, you can move up much faster etc
@SirCommandant, I wouldn't make Con San as an island battle doesn't feel at all like the Vietnam war to me. If there was any island battles, do it on one of the real ones.