It should have an holographic arc like grenades do in Gears of War. It has travel time so this wouldn't make it that much easier to hit anything. Also the arc should only be visible to you. This would help against installations and stuff.

As CCP themselves hoped, the plasma cannon was designed to be an AV weapon, and its hardly doing its job and not due to its power, but its mechanics. Issue is, they won't want it to be OP to infantry.
My question is, why is it a problem if its OP to infantry? In pretty much every other FPS, explosives and AV that effects infantry in general are always OP to infantry and vehicles, but its balanced by having a small amount of ammunition that can be carried, and the use of it taking up resources in some cases.
I think that its OK to have a borderline OP boomstick, as long as you make sure that they aren't just throw away, and rewarding players for properly using them (area control, and AV).
I think the way to make people use them, is to simply use a straighter flight trajectory (doesn't have to be faster per se), and make firing and reloading faster.
Its got everything else right; you only get 7 shots so people don't use it willy nilly, you get rewarded more for taking out vehicles, and its so hard to get a direct or near hit on infantry you can hardly use it against them.

In Short, Just straighten the flight path a little, and make reloading faster or add a magazine with a few shots.

In the weapon's description it says that it was meant a close quarters infantry weapon. You probably read somewhere online that it was an AV weapon, but do yourself a favor and actually read the description. It's basically a Rocket Propelled Grenade(RPG), in fact, the description mirrors this. Just because it can hurt vehicles, doesn't mean it was meant to.

You should focus on using it to do what it "can" do, like OHKO any scout with just its splash dmg.

Plasma cannon needs to be revamped completely:

Moved to Heavy Weapon Section
Given a 4 shot magazine
Faster projectile mps


Right now it is unused or utilized because it was never given much thought. It should be the Shield damage equivalent to a Forge Gun.

Plasma cannon damage over time effect
Game Design has considered this, but weGÇÖre not getting many resources for new code/features so damage over time is not going to happen any time soon. We canGÇÖt see any way to easily improve the Plasma Cannon against vehicles (its intended role) without making it OP against infantry, Game Design will address issues with the Plasma Cannon in the future.

Actually, CCP did state that its intended role is AV, and I'll even provide the link.

The link

Two problems with this logic. First I never saw anywhere that suggested it's an AV weapon by CCP design. On the contrary the description of the weapon states that it's CQC weapon, likely implying anti-infantry mostly - which is what it actually does reasonably well at the moment.

Second - gtfo: OP against infantry is fair if it's resource intensive? Dumbest thing I've seen in a long while: "you got one shot insta-killed by dumbfire noobtube - hey but's it's ok because it got only 5 more shots"