Honestly? I enjoy Tarquin far more then Nale. Nale was a one-shot joke of a character who has been stretched far to thin already by his pretentions of major villainhood - which would probably have been alright, if he hadn't continuously tried to insert himself vicariously into the foreground against the Order without pausing for breath. There's only a certain degree to which his 'Look at me, Daddy! I'm BAD!" brand of un-goaled evil can be tolerated, especially as it comes across with none of the wit or panache that even XYKON posesses in his megalomanical schemes.

Tarquin, by contrast, is not a villain in desperate need of a plot. He's already got one, and it's already been a success (by his terms) for decades. As a character he's interesting and likable, and as bonus, his own personal goals not only don't conflict with the current mission of the OotS, but he actively has a vested interest of his own to keep Xykon from conquering/Redcloak from destroying the world. He's a villain in the background material, yes, but in a sense he's not really a major villain of the OotS campaign. And whilst Rich could turn him into one, I don't really see how doing so would add anything to the story as a whole.

I'm personally hoping Tarquin sticks around long enough to be the villain of OotS 2: The Elan-focused sequal; and that Nale is the villain who gets 'Worfed' to demonstrate Xykon's power (if anyone really needed to be by this point n the game). Though I'd admit, Tarquin backstabbing Nale in a reflection of Nale's shanking of Elan would also make me smile in a 'just deserts' manner. But in the end, the plot is for Ritch to decide. And if he plans for Tarquin to meet his end by Xykon's finger of death two strips from now, I wouldn't object as long as it adds to the development of the ongoing tale.