Alright, I'm gonna take a crack at a OD system.
First no infinite stream OD, I say it's capped at 6-8 seconds. The stream OD would only be usable by Outriders and Raiders. Outriders would receive no health loss when it's in use, however Raiders will receive the health drain.
Burst OD would only be usable by Sentinels and Raiders, it would have a cooldown period after use (say, 3 seconds). Sentinels don't lose health when it's used, however Raiders lose health when it's used.
And here's my attempt at the 'lock on' weapon. First of all, I hated this weapon in Tribes 2, mostly because it made carrying flares a must and put a backseat on using the other available grenade types.
My implementation would be this: The 'lock' would still lock on to certain heat signatures (say, a Legionnaire activating his rocket or going into OD), and it would only sense the enemy's 'heat signatures'. To activate the lock, your reticule would need to be on the subject for 2-3 seconds while they're emitting 'heat'.
The weapon would only be available to sentinels due to it's large, cumbersome size.
The projectile itself would be large, slower in speed (average skiing ability would outrun it), and cause a moderate amount of damage. It can also be destroyed by gunfire, be it a well placed rocket, or several chaingun shots, it would be destructible.
It's also easy to trick, if a capper has a projectile coming in on him, a teammate can go into OD and steer the projectile towards them, instead of the capper. Basically, the projectile will follow whatever enemy is generating the most 'heat'.
I like this type of lock on weapon, because it's not overpowered (it has a lot of cons), but it's also useful for defense and offense, as it will decimate llamas (their jet signatures and slow movement would be an easy lock and hit for the weapon), but it's also not too overpowered against cappers. A well done OD cap and subsequent escape would easily be able to outrun the projectile.
Offensively the weapon would primarily be used against enemy base assets.
I would have to say this would be an interesting way to go at it as well. Even though the rocket lock-on would still be something to look into with the add-on of infi-OD (MAYBE) in the near future. Since it wouldn't be that hard to evade rockets through building if your an outrider, bit harder on raider to maintain the speed and keep OD, and sentinels would just be there to intercept the rockets (if/when used the right way) and the rockets would be able to be shot down as seymour has said up above. I dunno it's just my way of looking at things for the future.
But hey if we were to happen to get said lock-on weapons, then what about shields? For the Raider or Outrider class. Since sentinels are high in defense already.
Infinite Overdrive