I just started posting using Zappl and I'm excited about its potential. There are some people who are posting with alt-accounts to keep their Steemit feeds consistent, which I think is perfectly fine. Since my account is still pretty small, though, I don't think I'm going to worry about that and instead just focus on making sure the content I create for each platform is of high quality and best represents me.
I do think you're right, though - while I think Steemit has blazed a massive trail, we'll most likely be dealing with multiple different front-ends in the future, and Steemit itself might not be the main one the community uses. We're already starting to see that, and that's a good thing, since a decentralization of front-ends allows for more creativity and for people to interact with the blockchain in a way that they best see fit. What I do think will be interesting is to play around with the different front-ends to see how the content plays together in a unified feed such as on Steemit. One blockchain with multiple front-ends allows for a kind of unity of the mind that is not achieved by the current model of data siloing via disparate social networks.