Yosemite and Default URL Handlers – Edovia Blog:

Unfortunately, Apple is now blocking sandboxed apps to change the default handler for a particular URL scheme. This is why Screens is not able to set Screen Sharing back as the default handler. This change affects a whole bunch of apps that use to rely on this functionality.

The sandboxing rules on OS X have always been a source of difficulty, as some cautioned early on. At the time I felt that Apple would see the harsh edges and work something out with developers so that more useful apps could be in the MAS over time. I thought that perhaps they’d sort it out to the level that even top-tier folks would manage to get their apps in there (think Photoshop or Office).

The King Makers: Apple Takes Down an Indie Dev | rollinsio:

On September 26, Greg submitted what he believed was a valid compromise:  The click would take the user to the main Launcher app, and from there the app would call the appropriate action.

Apple rejected the update and within an hour Launcher was no longer on the App Store.