There is one simple thing Bungie could do to make these weapons worthwhile, all without changing any of their characteristics.

There's three specials that can go in the primary slot: Universal Remote, No Land Beyond, and Vex Mythoclast. The first two suck horribly. The Mythoclast is one of the best exotics in the game, So what's different? Well, for one thing, it acts and functions like a primary weapon. That's key.

Primary weapons are essentially your most used for the majority of situations. Specials are meant for… special situations. Heavies are meant for when you need to deal a ton of damage (all at once to few targets for rockets, and over time to many targets for HMG).

Is giving up the primary slot for something that doesn't act like a primary ever beneficial? I'd say not really. I'm struggling to think of a single situation besides maybe giving it up to have shotty snipers on a big crucible map.

If what's in your primary slot doesn't act like a primary, you are kind of hosed for most things. But what about the heavy slot? Would there ever be a situation where you might want to give up a heavy slot for another special? I'd say yes! Your heavy is the most infrequently used. Most of the time it's doing nothing, and you don't always have ammo for it. It's the most situational.

I would say that if Bungie changed these two weapons to take green ammo, but go in the heavy slot, that they would magically become useful. You could run shotty snipers (Universal Remote), or sniper fusion rifle (No Land Beyond), which I can see being of benefit in a bunch of situations.

Being able to hit hard close and far would make up for no heavy in lots of scenarios.