It doesn't matter characterwise. It was just one last insult to Stannis (and his fans, let's not pretend they are very respectful to any fans). They said they loved Renly and thought he would make a great king and hated Stannis.
Of course, as soon as they get to where the book material ends, Stannis burns his daughter who he loves very much without considering the many other options, pretty much everyone abandons him, he gets curb-stomped while making ridiculous rookie mistakes (no scouts, no formations), and dies in the name of Renly. It's clear that the "rightful king" bit was just one more insult to injury. As was Stannis's acceptance of the fact.
It was D&D's way of saying Renly should have been king and Stannis would have been better off accepting that.
I had a bit more, but the computer ate my response. So, here's the Cliff Notes version:
In response to those who say Sansa's Season 5 storyline was necessary for her empowerment, how was she empowered? The last episode had Sansa try to get someone to save her, accept death is better than current situation, and finally get saved by someone else. How is any of that empowerment? That's she's actively trying to get people to save her?
In response to bad shit happening to other characters, so? This is a Sansa Thread. I, and I suspect others, are pretty pissed about the other changes (it was Shireen's burning that brought me back). But this is a Sansa Thread. Talking about the shitty thing done to X doesn't mean there can be no empathy for Y.
In response to Sansa being free from LF, how? Seriously, being on the run without supplies and having armies looking for you is not freedom. It's being on the run.
I put this in the Rants section because I noticed it while I was writing up my rants.
Meryn Trant sexually abused Sansa. The girls he was beating did look a bit like her. His new inclinations retcon the whole "abuse Sansa because ordered" to "getting his rocks off while abusing Sansa."
I mean, I dunno. In some ways, it feels even worse than the rape. There was some sort of logical progression (I use logical extremely losely). But this just feels gratuitous. Unlike the rape scene, it doesn't even have shock value since people aren't going to realize it right away. It's purely to punish Sansa sexually.