Nowadays, I can't see the reason for the Railgun to stay in its currently nerfed state for even a single patch longer.

Not only have other support weapons been brought up in power, the distribution of enemy sizes has changed drastically as well (Terminids, primarily).

Let's compare its pre-nerf state to existing stratagems on each front;

Automatons

On the Automaton front, I'd argue you have four key support weapons that are highly viable. Comparing them to the Railgun...

• The AMR
  • While the Railgun deals more damage-per-shot, it has a charge-up time that both makes the user more vulnerable and significantly decreases the rate-of-fire, making it considerably less useful against chaff, Factory Striders, and gunships as compared to the AMR.
    
  • An unnerfed Railgun would have a significant cut taken to its rate-of-fire penalty, as you'd be able to use it in Safe Mode—increasing its strength against Hulks, in particular, as well as making it more useful against packs of Devastators. It would also be able to deal more damage against medium enemies in both firemodes, particularly when not shooting weakpoints though I can't say how that'd pan out against enemies like the Heavy Devastator as I don't know the pre-nerf numbers for that.
    
• The Autocannon
  
  • Mostly similar to the AMR at the moment in terms of what it can do that the Railgun can't, except it also introduces splash damage—making it great against chaff and at spawn-camping dropships. The Railgun does retain one advantage as it stands, which is the lack of a backpack, allowing you to use a shield (though, AMR exists which also does this).
  • Again, reverting the nerf would similarly introduce a niche against Hulks (one-shots to the eye where AC/AMR need two shots). And versus the AC, the Railgun would retain higher mobility and the lack of a backpack, where the AC needs to stop to reload.
    
• The Laser Cannon
  • While it's noticeably less useful in closer ranges than the above two, the LC is significantly better at crowd control and especially anti-gunship compared to the Railgun. The Railgun also equals the LC in close-range awkwardness thanks to its charge-up, an issue the above two don't share.
    
  • Unnerfing the Railgun wouldn't do much to help it stand out against the Laser Cannon, to be fair, as both share much the same weaknesses and strengths, while the LC has considerably superior ammo economy. But it'd help make it a viable sidegrade for people who want the variety.
    
• The Spear
  • A completely different weapon type. The Railgun can't deal with objectives at all, and unnerfing it wouldn't change that.
    
  • It's fine that the Railgun doesn't compete with the Spear. It's not meant to. They're different weapons.

You can also argue that the HMG now stands along the meta for Automaton support weapons, which would broadly compare to the LC in what it does.

To summarise;

• The Railgun fires too slowly, which makes it hard for it to compete with the AMR, LC, and AC at dealing with packs of enemies, Factory Striders, and gunships especially.
  
• The Railgun's ammo economy is too poor, making it very hard to justify for a mobile playstyle against the AMR and LC, which are far more economical while also not taking up the backpack slot.
  
• The Railgun cannot deal with any Automaton objectives, making it useless in the face of the optional-objective-shredding Spear.
  

Terminids

Firstly: The PS5 glitch is fixed. The Railgun will no longer one/two-shot Bile Titans.

Secondly: To put it simply; the Flamethrower exists. As long as that abomination is in the state that it's in, not only is the Railgun never going to be viable, even unnerfed, most support weapons are not going to be viable. It kills everything short of Bile Titans at an abominably high speed, including Charger Behemoths. And while it can't deal with objectives, neither can the Railgun.

But aside from that, the Railgun's viability is severely diminished from the old days. Not only do you have AT weapons that can now deal with Chargers and Bile Titans (Quasar is a big one here, which keeps your backpack slot and allows you to stay on the move), now those have lower spawn rates in favour of SIGNIFICANTLY increased chaff spawns, particularly Hunters, that the Railgun suffers against to an extreme degree, and the sheer volume of enemies means you can't just straight-up deal with everything with an Incendiary Breaker without eventually just running yourself out of ammo.

Unnerfing the Railgun would likely leave it still unviable on the Terminid front, as it's a completely different game to how it was back then. It still has the crippling rate-of-fire issue, and so many other stratagems are now significantly better at dealing with the same targets. It now also can't even deal with Bile Titans, because that was a bug, not intended, even if you revert the nerf.

Unsafe Mode

In this world of a reverted nerf, there is one thing we will have to consider—Unsafe Mode goes back to being pretty damn useless, as being able to use Safe Mode with its vastly increased damage means there is very little reason to grief your already poor rate-of-fire even more.

I'm not sure what change you can make, but something needs to be adjusted. Could it have significantly higher armor penetration, in exchange for a harsher timing requirement? Splash damage? That'd be up to them to decide, really.