Twitter CEO Dick Costolo recently sat down with The Wall Street Journal for a relatively-rare interview, and while the conversation unsurprisingly spends some time on an IPO (Costolo says "it's not necessarily inevitable"), the CEO did offer some thoughts that are worth pointing out. Concerning the company's recent Vine launch, Costolo says that after Facebook beat Twitter out for Instagram, the company didn't want to copy the photo service but instead was "looking for the next thing." Vine turned out to be that thing; Costolo calls the six-second videos "hyper-constrained publishing" that will "force people to be creative and foster this new art form." We do question the sentiment that "we're not going do what those other guys did" considering Twitter's Instagram-aping image filters, however.

Looking more towards the future, the CEO says one of his primary concerns is that its employees will fear big changes and instead focus on incremental improvements, and he realizes that Twitter faces a learning curve battle. He hopes to get a billion users onto the service, but for new users the world of RT's and @ mentions isn't accessible: as he says, "you have to invest, frankly, too much to get that 'aha' moment." He believes the new weekly email digests highlighting top tweets will be a big step towards convincing users that are first trying out the service to start incorporating it into their daily workflow. You can read the full interview here.