There are a couple of weapons from other games that GTA Online could take inspiration from.
Many games share concepts when it comes to weaponry. GTA Online already shares plenty of weapons with other games, like the Stone Hatchet in Red Dead Redemption 2. Even the common pistol has been seen in practically every game.
Of course, there are also some weapons from past GTA titles that would be nice to see again in GTA Online. Sometimes, weapons are removed for being inefficient or for not fitting the game's mechanics (like dual-wielding). However, that doesn't mean that a future update can't remedy that if Rockstar Games truly wanted it.
The weapons listed in this article are unlikely to be added to GTA Online, but they are still fun ideas that are worth discussing.
Five weapons GTA Online should borrow from other games
#5 - Dual Pistols
Dual pistols may not be practical, but one cannot deny how cool they look. GTA San Andreas players already have the ability to wield dual weapons.
Game series like Hitman also allow the player to wield two pistols, so it isn't entirely unheard of in principle.
#4 - Mollusk Launcher (Saints Row)
This idea would be more unique to the GTA world, but a weapon that can control the minds of NPCs for a while would be interesting.
It's terribly unrealistic, but GTA Online already crossed that line a long time ago, so it wouldn't hurt to push it even further.
#3 - Dynamite
Dynamite is already in another Rockstar Games title (Red Dead Redemption 2), so it wouldn't be impossible to borrow the code for GTA Online.
Alternatively, Rockstar could try to make the Dynamite easier to shoot with a sidearm, allowing an instant explosion similar to Ashe in Overwatch.
#2 - Flamethrower
The Flamethrower was available in past GTA titles, but it is strangely missing in GTA Online.
It isn't the strongest weapon around, but it could easily be buffed to have a niche as an anti-armored vehicle weapon. This could help the Flamethrower differentiate itself from the usually superior Rocket Launcher, although having a fun yet impractical heavy weapon wouldn't be the worst thing either.
#1 - Tesla Gun
Futuristic game series, like Ratchet and Clank, often have futuristic weapons such as the Tesla Gun.
GTA Online already has historic weapons like a Stone Hatchet that grants immunity to death for a while if used properly. Having a futuristic weapon shoot electricity would, therefore, not be out of the ordinary. Plus, GTA Online already has futuristic weapons like the Up-n-Atomizer.
Note: This list is subjective and reflects only the writer's opinions.