What about mods? Even though PS4 might get mods for a game or two, most of the good PC RPGs have tons of mods.
Mods for: Skyrim, Oblivion, Morrowind, Fallout 4, NV, 3 - see
www.nexusmods.com
PC-only: Divinity Original Sin
Do you like isometric / top down RPGs?
Shadowrun Returns, Wasteland 2, Pillars of Eternity, Baldur's Gate remake
Gog.com: D&D games, Fallout 1 - 2
Did you ever play Star Wars KOTOR 1 - 2? Even if you did, you might want to have a PC to play the KOTOR MMO for all the single-player RPG content
Edit: you might want to wait a little while, since nvidia will be releasing their new cards soon (June?) and this will be the first die shrink in years. Or build with an old/used card as a placeholder and play through some of the older games while you wait.