So, looks like the Steam re-release will be an updated version of the game and a completely different application. Should it have a dedicated page to separate it from the original? Something very similar has alredy been done with games like Crazy Taxi that has a "Crazy Taxi (Steam)" page.
Topic on Talk:Hellgate: London
Why did we gave "Crazy Taxi (Steam)" it's own page?
The question isn't why it got its own page (as that's understandable given the 12 year gap and updated version). The question is why it was named (Steam) and not (2014) which IMHO is more accurate.
Anyway, I'd say that it depends on how much is actually changed in the re-release. If "enough" things are different, then yes, a "Hellgate: London (2018)" article can be created instead.
If the changes warrants a separate "Hellgate: London (2018)" article, either a disambig tag and/or a series box can be used to separate the two from one another.
For examples, see "Naruto Shippuden: Ultimate Ninja Storm 3 Full Burst" and "Naruto Shippuden: Ultimate Ninja Storm 3 Full Burst HD", where the latter is a HD DLC version of the former that necessitated another article.
In fact, I'd probably recommend a separate article because there's no direct ties of the old version to this new one (e.g. players can't upgrade from the old to the Steam re-release). It is essentially a re-release and slightly changed version of the older game, hence it should IMHO have a separate article