What do you think of Stannis’s offer to name Renly as his heir at their parley? Do you think he thought there was any chance of it being accepted? And if he did accept it, how do the Tyrells react? For that matter, I imagine Selyse wouldn’t be too thrilled.

It was both remarkably generous and completely inadequate to the situation. The basic problem is that both Stannis and Renly have committed to diametrically opposed positions. 

I don’t think he thought it would be, but it was as far as he was willing to go.

And the Tyrells didn’t seem to care, in OTL.