It's easy to get the idea Jack Dorsey is acting out a revenge fantasy. Fired one year ago as CEO of his brainchild Twitter, Dorsey now says he's planning a startup with "similar ideas" — right in Twitter's back yard.

There was chatter in recent months the bi-coastal Dorsey (pictured) might plant his forthcoming venture in his second home base, New York, or even in his childhood home of St. Louis ("St. Louis will play a very large part in its story," he said of the startup last month).

But we hear Dorsey's been hunting for office space in San Francisco, Twitter's stomping grounds. He's hinted at as much on his Twitter stream: "I think we just found awesome office space," he wrote, just a couple of hours before he was "standing outside the... office" of SF-based Zendesk.

Dorsey's new startup is in "stealth mode." Since that's just Valleyspeak for being coy, we still know plenty about the company: it would enable person-to-person electronic payments via iPhone, MG Siegler wrote in TechCrunch this past spring, and the company has been awaiting regulatory approval, according to the St. Louis Business Journal.

It's a good idea; in fact programmer Max Levchin created the same capability for the Palm Pilot, the iPhone's old ancestor, before he and his co-founders expanded the idea into the financially successful internet-wide payment system PayPal.

So why is Dorsey framing his payments company as a new iteration of his old microblogging startup Twitter, of which he remains chairman? Dorsey told a St. Louis audience his company would have "similar ideas" as Twitter but "in a completely different industry," according to Nick Lucchesi of the Riverfront Times alt weekly. Is Dorsey hinting at additional publishing capabilities no one knows about yet?

More likely, the man who has said he would "never leave Twitter" is just extracting some free hype from a brand that clearly remains his baby, as far as Dorsey is concerned. In this regard, the prototype Twitterer thus remains the quintessential Twitterer: always self promoting.

(Pic by Esther Dyson)