I don't see them building in twitter support any time soon, and if they do, it would likely be in iChat instead of Safari. You also forgot to mention them implementing text expanding capabilities. Text Expander just lost a lot of potential customers. (I'm still using the free "Textpander" version before they sold the app. Hopefully I'll be able to ditch it with snow leopard.

Things I could see them implementing.

1. More features from Quicksilver ...better keyboard app launching
2. A better password/secure info manager like 1Password (upgraded keychain)
3. Better app removal similar to AppZapper/AppCleaner
4. Full FTP support in the Finder.
5. better Dropbox like sync in mobileme
6. better control over burning discs (bye bye Toast overkill)
7. better font management