I grew up playing Runescape before World of Warcraft, and always loved the high fantasy theme. I'd love a single player game, fantasy style, with Runescape like aspects. The colours, the elements, the warrior/archer/ranger, the music. One thing you have to say is that the Runescape music really worked for us as kids back then.
Perhaps not the grind.
But the high fantasy atmosphere is something I wish I could experience again.
I want this as well. I loved Runescape as a kid and OSRS is fun, but it really doesn't feel like I'm the target audience anymore.
One thing I've loved is their concept of Leagues. I would love a game like OSRS that has a persistent mode and a sort of seasonal Leagues type mode.
Also a game with improved running mechanics. Running feels awful compared to other games you can play these days.
And improved PvP; the wilderness is a cool concept, but I think it would work better to have a duplicate world "underneath" the regular world that's the exact same but with faster xp and rewards along with the risk of player killers.
Also better afk-ability, since the game is meant to be played over extended periods of time.
Supported macro-ability and better inventory management?
These things will never end up in OSRS because they'll ruin the way the game has been played, but I really want a game that checks these boxes.
Perhaps not the grind.
But the high fantasy atmosphere is something I wish I could experience again.