IMO sandboxing on desktop is failed attempt. Browser is a sandbox platform. Nobody will download some shady application and run it, even if it's sandboxed (but a lot of people don't really mind to visit a shady website).
If an application is in AppStore, it means that Apple got some legal documents from developer, it means that Apple performed some automated scans on application binaries. For me it's enough to have some trust. Sandboxing is not needed and it actually making some apps unusable or even impossible to implement.
Desktop apps always were in control of the entire computer. And they are now, unless you are downloading them from the AppStore. That's why a PC is much more useful than an iPad or iPhone for power users.
And it's not as if non-Sandboxed applications won't be used. They'll just be distributed outside the app store. So all of the potentially "dangerous" apps are one-more-step removed from Apple's oversight and ability to pull the app and halt downloads. Gatekeeper gives them some power in this regard, but what's the point of not allowing them in the Mac App Store? Is the PR from having a keylogger in the MAS really that different from the recent Instagram password harvester for iOS, or a Mac keylogger that was direct-downloaded?
If an application is in AppStore, it means that Apple got some legal documents from developer, it means that Apple performed some automated scans on application binaries. For me it's enough to have some trust. Sandboxing is not needed and it actually making some apps unusable or even impossible to implement.
Desktop apps always were in control of the entire computer. And they are now, unless you are downloading them from the AppStore. That's why a PC is much more useful than an iPad or iPhone for power users.