To be honest, I don't think it is really. Its all a matter of how people prefer to communicate or roleplay. I've been wanting to start up Twitter RP's with people and get a nice feed going, however, some have said its just a huge chat killer. It isn't really what has killed chats in the past. Lets take a look at the PKMN Crossing chat long ago. The strict rules and fear of getting the ban hammer for a small mistake or comment is what drove people away and ultimately killed that chat. The Armonia chat was cited by the staff to be dead even before Twitter RPing started. I'd go in there and there would be 6 people sitting in silence. People just stopped going because the chats are dead, which includes many of us who are mostly using Twitter. Many of us concluded that PKMN Armonia would be dead if Twitter RPing didn't help reinvigorate interest among people. People say that Twitter is what kills chats, but the harsh truth is its really what goes on in the chats that do. If there's no issues and plenty of activity, people will stick around a chat.
Some people don't like Twitter RPing and all, because they prefer more detail in RP's. The 140 character limit doesn't allow for the mass detail that many love to write. Twitter is not for everyone and that reasoning is fair. Some even find it difficult to do. I saw it though being treated as if it is a plague to groups and it kills the groups. In PKMNSkies, the chats are full of activity and honestly, I doubt a group of 230+ people would die if people began to RP through Twitter. I like how the chats are, and I wanna use them more. I know the mods don't wish to utilize Twitter, though, which is understandable. I'm not saying at all that Skies should be a Twitter group. The group is fine the way it is. In the end for RPing, though, its all a matter of preference really. Some people are intimidated by large group chats or large group RP's and might find comfort in Twitter RPing. I know a few who don't enjoy large chats, but find Twitter more comfortable to use for roleplays. Each method of RPing has its advantages and disadvantages. For Twitter, its quick easy for some, mobile, and not as intimidating for people who don't like large group chats. There is the issue of the 140 character limit, though and some may find it more difficult.
Everyone has a preference for how they wish to RP, like some don't like to use notes. Its completely fine if you don't like to use Twitter for RPing, or the chats even. Like I said, everyone has their preference for what they're comfortable doing. I don't wish to start an uprising though that would suddenly drag people away from a chat room and onto Twitter. I actually doubt that if a select number of people started using Twitter, it would completely kill a chatroom. I'm not too fond though of some of the things I have seen being said and how some almost look down actually on those who use Twitter. I actually felt attacked for my preference so I just left the chat. It seemed to me also as if some were saying how you can and can't RP. Anyway, I want to make it clear that I do love the chats and all and I understand that a group like PKMNSkies will not become a Twitter exclusive group. The group is fine the way it is. If people don't wanna make Twitter accounts and join in with some of us, that's completely fine! I don't want to start any trouble really and I just had a thought that I needed to voice after many of us discussed this because of the very negative views on Twitter RPing and how it feels like some look down on some of us.
To sum it all up, no I don't think Twitter is a chat killer and its all a matter of personal preference.