Why should they be pointed out to you as a player?
Playing the game and learning from experience should net you the skills to handle any situation cautiously before you dive into the skirmish. Having it pointed out to you isn't doing you any favors.
Here's to hoping the plasma rifle is fixed. I've been asking for it be fixed for 3 games now 343i.
That's silly. If that's the case, why not just replace every weapon model with the assault rifle, and let it be a surprise when the dude starts shooting rockets at you. Visual cues about the enemy and their threat level are a fundamental part of any intelligent FPS.
Part of what separates Halo from dreck like CoD is that there's strategy in every encounter, it's not just a matter of 'see dude, shoot dude before other dude shoots you'. Every element of an encounter, from the weapons I have, to the weapons I see on him, to my position on the approach, to the proximity of other enemies or allies, plays a part on whether you choose to engage, how you engage, and whether or not you come out on top.
If there's no way of knowing what abilities or bonuses a player has, then there's no what of measuring the situation effectively and strategizing on the fly. I don't need a giant sign or warning telling me everything about every enemy, just some visual cue as to what loadout they're running.