I actually have plans for "anti-matter ammo" for high explosive damage for plasma weapons (basically anti-plasma in a containment field, hitting something breaks the field, matter-anti-matter reaction -> BOOM), which would be unrecoverable, so inaccessible to XCom. This would be the aliens' answer to XCom's armor tech, but the clips are unstable and XCom can't handle the anti-matter. Roughly, it's still in the "stuff I dreamed up once" category
The alien grenade in small launcher mod is interesting, although I'm not sure if it could work in OpenXCom. To me, it's about the same thing as the Elerium Bomb already developed by fatrat (except you can't prime and throw those) and also present in the Alien Armoury Expanded.
Adding Elerium Explosives by delaying XCom Blaster Launcher access does give something to the aliens: They don't get blasted for a while longer, they are only getting "mildly blasted" for that time (during which time passes by, so tougher races become more likely to spawn and they can handle the blasters better). I don't think it needs to give them more.
I agree very much regarding mods, mileage will always vary. I design mods for myself/people who like the same stuff as me, ie more options but longer/harder games and a customizable experience (not a mega mod). Using that, someone who wants it easy mode/quick can also enjoy part of what I created, and some masochist can use only the parts that make it harder too.
Having talked/thought about this so much, now I really should just put it in the XAE.
@Solarius: I like the idea of an improved missile-launcher, but I feel like that's best handled by the blaster launcher. I thought about making one but could never decide what to use. Maybe Large Rockets, Elerium Rockets and Guided Missiles could make a good set of ammo..
@LeBashar: I have Elerium craft weapons and I would tend to agree that they are not that great. The main thing is that they depend on the Elerium Bomb which is incredibly hard to get, somehow.. Adding Elerium Explosives might help with that. I see them as the weapons you put on a few of your toughest vessels, to engage battleships and terror ships, before you have access to the Blaster Launcher craft weapon. Also, many people intend to address the laser rifle/heavy plasma so that they are no longer overpowered. The issue is with the Heavy Plasma, because nerfing it nerfs aliens... I am considering making a new line of "human plasma weapons", to be able to address that.