I'm not a creative person, but I always wanted to see a rune knight (because the rune fencer was taken by red mage...), but I do imagine it like Kalocin said. Outward gives a great example and we already have ninja having the ninjutsus, so why can't we have runes work like ninjutsu? It'd create at least 6 skills easily. For instance we could have a rune for attacks (let's call it 1), a rune for defensive cooldowns (let's call it 2) and a rune for utility for the party (Let's call it 3). We could have a secondary rune to be used when we make combinations for the rune 1 in a way that the attacks become AoE. So let's say 1+2+1 (starts being an attack) could be like you said, a DoT. 1+1+1 basic rune attack combo, and so it goes. Like I said, I'm no quite creative but I do think the ninja skills are quite a good inspiration because he really fits an "magic swordsman" vibe, as he uses way more magic skills than physical ones. Oh well.

Also, for the Dark Knight thing, I REALLY still think they should like good ol' FFs and make him use health (like on PvP) instead of magic. There are many ways to make it viable, they're just scared of making the job hard.