Rather than all ammo based weapons taking the same generic ammo, I'd really love to have some options.

Rockets that are...
Faster but have lower damage
higher damage but smaller prox fuse
Massive damage but no prox fuse.

Explosive rail gun rounds

etc... etc...

Yes, please.

Oh hell yes!

+1 but what would the implementation look like?

Would ammo be purchased the same way addons are now? Would the ammo be specific to a given launcher such that every launcher would have something like 5 unique variants? And if you have 2 or more of the same launcher equipped, how would determine which ammo gets loaded into which launcher?

A simpler approach might be to have an ammo selection dialog pop up when you click the reload button, therefore only needing to show ammo compatible with the currently installed launchers.

Which brings up another question of would the selection of ammo available vary by station? (I assume all stations would at least be able to sell the basic unmodified variant). And what about reloads from capships? Would all variants be available for reload there?

And what about capacity? Would the max number of rounds loadable vary depending on the ammo type and what would determine the number of rounds that could be installed of a given type? Would it be by volume, mass, some other metric? The simplest approach would, of course, be to keep it all the same qty per launcher.

Finally, would you be able to mix two different types of ammo in the same launcher? I assume not because that could get to be complicated, but if mixing is not allowed then what about reloading a launcher with partial ammo left? Unless there is a way to sell off the partial ammo remaining or unload to inventory, then the player would annoyingly have to launch from the station and shoot the remaining rounds before being allowed to change to another type.

EDIT:
One more: The player would need a way to determine what ammo is loaded in a given launcher when assigning weapon triggers, especially for the case where there are multiple of the same launcher installed, each with different ammo.

Launchers could be the equippable items, seperate items for ammo and you load the launchers with the items kind of like a special inventory slot. Unfortunately this is unlikely to be developmentally simple based on my knowledge.

Small port high capacity launcher - 50 Standard shots
Same weight as sunflare launcher

Small port med capacity launcher - 40 Standard shots
Same weight as starflare launcher

Small port low capacity launcher - 30 Standard shots
Same weight as iceflare launcher

Sunflare rocket - 4 standard shots each
Starflare rocket - 3.5 standard shots each
Iceflare launcher - 3 standard shots each

You could then add different types of rockets into the mix, and yes, mix and match the rockets in a launcher and have them fire in the same sequence (since its a rocket tube).

Small port low capacity multiple rocket launcher - 30 Standard shots
Same weight as starflare launcher
allows you to bind different ammo types

then you could add something like this for diversity

This implementation would slightly exacerbate the weight problem because you'd be able to fit 7 sunflares in a light launcher so I guess a base weight + per ammo addition of weight could be justified, but then you start to get into really complicated territory.

It would be ideal if each shot reduced the overall weight of the ship, but thats also a major major project to screw around with.

Also, Napalm rockets that catch your ship on fire and catch other things you run into on fire! Let's go all Descent3-style on missiles and rockets! :D