[bitwize]

Game modding is going to go away almost entirely soon. The vanguard here is Capcom. They have gotten a bit uncomfortable with modders who do things like put Chun Li and Cammy in bikinis, not to mention the possibility for cheat mods. Accordingly, they now consider modding to be the equivalent of piracy and have implemented mod-preventing DRM in their back catalog of PC games.

Other companies will soon follow. There's too much risk to a company's bottom line and reputation to allow or encourage modding. Mods compete with official DLC packs, and if someone streams with, say, a mod that puts a swastika on the main character or something, that harms the publisher's reputation.

I would say hang on to your old copies of Doom and Quake... but Doom and Quake are Microsoft products now, and Microsoft doubtless has ways to make the asset packs unavailable except to official ports which require a Microsoft account to play.