Eh?
With respect, Steven, I think you’re wrong? Renly absolutely does offer Catelyn (who is speaking for Robb, so he’s offering it to Robb) the right to call himself a King while still being a de facto lord.
From Catelyn II, ACOK:
That’s not the deal Renly offers Catelyn in the books, only in the show.
Renly’s offer in the books is: see how I destroy my enemies, join me or I’ll do the same to you.
“He can even go on calling himself the King in the North if he likes, so long as he bends the knee and does my homage as his overlord. King is only a word, but fealty, loyalty, service… those I must have.”
That seems like an offer to me?
Accountability Corner Time!
Yeah, you’re right. I answered that ask first thing on waking up and wasn’t paying close enough attention. I should probably wait to reply to asks until I’m fully alert.
So to give it another pass: I would say that Renly’s offer is a largely symbolic one, and doesn’t really deal with some of the material issues – Robb’s vendetta against the Lannisters, whether or not he’s the overlord of the Riverlands, any of the war aims Robb put forward, etc. – necessary for a Dornish Option to work.
Moreover, the sincerity of Renly’s offer is somewhat undermined by his actions in Catelyn III when he refuses to allow her to leave so that “you shall see what befalls rebels with your own eyes, so your son can hear it from your own lips.”