Best I can say is well given Steam cuurrently has the soundtrack up for sale ans G.O.G doesn't(usually G.O.G or the studio/devs are abit slow on updating or even adding add-ons onto the listed page kinda just depends on what the hold up is really onwho is to blame in a case by case basis) So I figuire the Addon will show up latter on as the Soundtrack willmost likily show up here too .. But I am aware of cases where for some reason studio's and/or companies make it so a person has to buy a more expesive version// Yet that scenerio I meantion from what I can find is a rarity to happen and when i does its the studio or company that decided it ..

So Yeah I'd say if you wanna have more money for later sales this month or would rather pay for the add-on and such later on here then go for the standard version as at the very least you get a whole game on the standard addition including the O.G add-ons.. And well if they don't end up showiung up here after about a year(sometimes DLC's and such take a long time to show up here but its kinda rare.. longest usually is a month wait for stuff other platforms get but rarely does a game's new stuff take a year to show up here) Then iether snag the Fate edition when dirt cheap or get the upgrade option if it shows up on here later(sometimes the upgrade option never pops up but thats a rarity too for a never happening thing)

Edited in Hope this atleast helped you in deciding to by one version or the other