That's an extensive list. There's some good ideas and some crazy ones. For what it's worth, here's my feedback:
This is really just a cosmetic change to the FAL that's already in the game, I don't think it needs to be a different weapon. The FAL we have can do everything that can.
This is a prototype that as far as I know never went into production and is not used by anyone.
The SRSS is also a prototype marketed primarily at civilians and police agencies. I'm not aware of any military units even considering it. A better option here would be the Desert Tech MDR, which still isn't used by any military force, but is at least a unique rifle rather than a conversion kit. (It's also not an assault rifle, this would be a Marksman weapon).
Maybe. It's a little out of scope for the game, but is used by Saudi Arabia so it's not entirely unlikely for it to show up in the type of conflict Sandstorm portrays.
This is a good one. It's a standard service rifle used by several NATO armies. While in some sense it is "just another 5.56mm rifle" it does at least look a bit unique.
This one gets asked for a lot. There's not much point, it would be nearly identical to the existing M-4A1 or Mk.18 depending on barrel length. This is a better option for a mod, and I'm sure someone will make one.
This is just a prototype at this point, it's not in production, and not used by anyone. It might (probably?) replace the G-36 in German service, but that's several years out at the earliest right now.
Yah, this is technically already in the game, you can use it offline using the console commands. Don't know why it hasn't been actually added yet, it may be with one of the coming updates. It was a favorite of a lot of people in Insurgency 2, I'm surprised it hasn't made a formal clearance yet.
The AK-74 is already in the game. An AK-74M would be cool, but could just be a weapon skin or mod.
I'm not sure what you mean by FN-MTAR21. The image you used is a CTAR-21 Tavor, made by IMI not FN. The Tavor is planned to come to Sandstorm in a future update.
Another incorrect attribution to FN - the XM-8 was made by H&K. It was only ever a prototype, though it advanced quite far into production, it was never acquired by any military for service.
Only ever made for and marketed for civilian use. Not in use by any military anywhere in the world.
This would be a neat addition to the game, though with the VHS-2 in the game now it would be a bit redundant. I think I'd rather see the AUG added for another 5.56mm bullpup service rifle, since it's more visually unique. Both would be within the scope of the game though.
Any number of various 9mm AR conversions could be cool. But there are so many other unique 9mm SMGs out there, I don't think we really need another AR in the game.
CA? Should be CZ. This is the sort of thing I was talking about above: I would LOVE to see a Skorpion Evo in the game. It would be far more unique and cool than any AR varient. The SIG MP-X would be another good choice for this roll, but I'd prefer the Skorpion. Also, it should be the full military version, not the silly arm-brace pistol version for US civilian use you have pictured (though, I really want one of those for myself IRL).
I'm not sure this is in scope for the game, but it's unique enough to be interesting. I'd use it.
We already have several variants of MP-5, I'm not sure what an MP-5K would add. That said, like the Galil it is in the game files and was in Insurgency 2, so we might see it later.
Prototype that never went into production.
We already have one of these in the game.
Another prototype that never went into production.
Not H&K. The MP-9 is made by the Swiss company Brügger & Thomet, who purchased and modified the TMP design from Steyr in 2001. I'm not sure how useful a compact machine pistol would be in Sandstorms more open spaces, but it could be fun to have.
If the MP-9 gets added, this would be a decent Insurgent equivalent.
It's a cool design, and fun to shoot, but it's not really in use by anyone at all, much less anyone who would reasonably be in the middle east.
Yup, this would be a good one. There's another thread on here specifically talking about adding this. It would be cool and unique, while still being a pump action.
I'm not sure what could possibly distinguish this from the 870 already in the game. They barely even look any different.
Same as above. Though if you mean a stockless version, eh, maybe as a breaching specific weapon, but otherwise fuck shotguns without stocks. They suck.
Another great gun that I would love to see added to Sandstorm. There's been lots of discussion over the gameplay dynamics of semi-auto shotguns, but I'd love to see them.
I'm not sure where "SASG" comes from, but the Saiga-12 would be the obvious choice as they Insurgent equivalent of the M-1014.
The UTS-15 is a prototype, not in use, and as far as I know has been an abysmal failure due to uncorrected reliability issues.
A good option, it could even be added as a pump only gun so as not to offend the people who think semi-auto shotguns would be too powerful. It's unique and iconic.
My initial thought is "oh god, no" - but it could actually be pretty fun as an Insurgent weapon. Though, brace for complaints about incredibly long reload times.
This would be pretty cool, especially if the P-90 were added. It would be a unique and different gun.
FNH TACTICAL, FN-X45, H&K-45, SPRINGFIELD XD-45, BARETTA PX4 STORM, KAHR CM-9
All good options, but I don't think any of them would bring anything unique to Sandstorm. We already have a bunch of pistols that perform almost exactly the same.
This would be pretty interesting as a Security Adviser weapon. Not sure what the Insurgent side one would be though.
.45 SAMURAI'S EDGE
There aren't presently any .40 pistols in the game, which seems like a missed opportunity with the number of nearly identical 9mm pistols we have. The USP is a reasonable candidate to add a .40 gun.
HI-POINT (For insurgents)
LOL. that would be interesting.