Let me first be clear: I am not railing against Twitter, in the manner I might against Facebook. I find Facebook’s business model creepy and intrusive. I find Twitter’s, er, saddening. I don’t (yet) believe that Twitter is doomed, but if it turns out to be so, then I think this is clearest sign of what will kill it.

So, here’s what’s happened – Twitter are making changes to their API that will affect how third party apps work. I honestly have no idea how this will play out over the long term, but here’s the nub of the problem:

This chart here is one Twitter have produced to explain what they want their API to be used for. The would like it to be used for things in the left and bottom quadrants. They expressly want to limit “certain uses” of things in that top-right quadrant. Which is, of course, the stuff that allows their users to interact with Twitter, every day. They are very clearly and unambiguously saying that encouraging consumer engagement with their service is not their priority.

And I’m not surprised. It’s not where the money is, as Twitter is currently structured. But it’s hard not to see this as a bait-and-switch on their users, and on the developer community that have helped those users engage with Twitter.

Like I say, I don’t know what will happen, but this sounds to me like Twitter saying “We wish to serve out customers better, and out customers are Brands. We are in the business of delivering people to Brands, not in providing services for people.”

For all I know, this will work just fine, people will adapt, and life will go on. But if my fears are true, I personally hope it won’t, in just the same way I hope Facebook will one day die.

Meanwhile, app.net are trying to launch a service that really isn’t making any pretence of being anything other than a paid-for Twitter clone.

The problem I can see with them is they’ve set a very, very high barrier to entry. I’m hoping it’ll turn out that the $50-a-year price tag is basically an early adopters thing, and somewhere down the line, they’re going to roll out a $5-a-month price tag, or even some kind of free/paid service options, because yeah, as it stands right now, that entry bar basically guarantees that it’ll be rich (in relative terms) nerds using the service, which will kill it before it gets very far out of the gate.

I’ve ponied up the cash, because I am (in relative terms) a rich nerd, and I’m really hoping that this cash will be seed capital that will produce a new Twitter-like service with a business model that profits from the engagement of their users, rather than the engagement of brands.