This is the response Tweetro's developer got from Twitter after he reached out because he hit that 100k user token limit. Tweetro is currently the only Windows 8 Metro Twitter app I know off:
“Thank you for reaching out to get clarification on our developer policies. As you know, we discourage developers from building apps that replicate our core user experience (aka “Twitter clients”). We know that there are developers that want to take their passion for Twitter and its ecosystem to unique underserved situations. As such, we have built some flexibility into our policy with regard to user tokens – which went into effect September 5th, 2012.”
“…Unfortunately, It does not appear that your service addresses an area that our current or future products do not already serve. As such, it does not qualify for an exemption.”
More in Richard Hay's piece on WindowsObsever.com
Marco Arment translates this to:
In other words: “Even though we don’t currently have a Windows 8 client, we might have one in the future, so yours isn’t allowed.” /.../
Now we know: “work with us directly” means “die”.
I've said this before but this pretty much also means Android tablets will never have a good Twitter client. Which is something very much missing in the Play Store, with currently a similar amount of apps available as Apple has in its store.