Evan Williams wrote recently that the future of identity belongs to Apple and Google, and I think he has some interesting thoughts. I definitely agree with him that Apple and Google have a leg-up on all the other potential identity providers (ahem: Facebook, Twitter). Most importantly, Apple and Google have woven their concept of identity deeply into the fabric of their mobile devices. And that’s the most important part.

(By the way, if you haven’t read his other piece on the five elements of identity, go ahead and give it a look-see. It’s well worth the read.)

But that deep integration into the user’s primary mobile device isn’t quite enough.

It’s great if my iPhone works as a communication device, and as a geographical locator. And it’d be cool if I could flash my iPhone (instead of my drivers license) when I walk into a nightclub.

But what about when I’m using other devices and services? What happens when I’m using my Blackberry PlayBook (yes, I have one) instead? What about when I want to log into my Netflix account or check my GMail?

There are two components here that I think are both missing from any potential AppleID: ubiquity and openness.

Throughout its history, Apple has always been happy to trade ubiquity for style. Not everyone has an iPhone, and that’s part of the appeal. By marketing their products toward the tastemakers, they’re making a calculated decision not to pursue the mundane consumer.

But even if you could make the case that Apple products are ubiquitous enough for them to launch an identity service, that’s still not enough. Ubiquity may be a prerequisite for launching an identity service, but openness is the true measure of success. And I can’t fathom that Apple will ever launch a truly open, platform-neutral, device-agnostic service.

Apple is addicted to lock-in. And they’re not about to give up their lock-in strategies to launch an open service.

If anyone at Apple really ever hopes to own Identity (with a capital I), they’d need to provide support for their platform in a way we’ve never seen from Apple. They’ll need an open protocol (truly open; not like the open FaceTime protocol that never really materialized) as well as reference implementations on all major platforms. When the rubber hits the road, can you actually imagine Apple implementing an identity app with an identical implementation for iOS and Android? Windows Phone 7?

Yeah, neither can I.

And that’s why your AppleID won’t ever matter.

Apple will never be your main identity provider.