iOS 8.3 beta 4 that was seeded to Apple's registered iOS developers last week has removed the long-standing option to share content to Twitter, according to our own findings a couple days ago that have since been confirmed by other users.
We've noticed something was afoot as the option to share to Twitter has gone missing from the Share sheet in iOS 8's stock Photos and Safari app.
Technically, the feature has not been removed entirely because it only disappears after installing Twitter's official iOS app in iOS 8.3 beta 4, as evidenced on the screenshots provided by our own Oliver Haslam.
Uninstall Twitter and it comes back.