Well you'll have to if Apple decides that ARM MacBooks will only be able to install apps from the Mac app store - they already have a precedent in iOS and precedent of pushing developers to do things their way.
iOS had a very different history with developers. The desktop isn't the mobile space.
Desktop developers have their own solutions in place and have for a long time. You'd be forcing them to give up a ton, in exchange for nothing of value. I'd expect many would just stop developing applications at all instead of comply with store requirements as they stand right now.
That's not to say those problems couldn't be resolved in the future.
All nice and good, and where would those developers go, considering that both Google and Microsoft are following similar sandbox approaches?
Those developers can choose between stay in business or go broke, because I doubt GNU/Linux or *BSD users would pay for desktop software as their current Mac OS X customers.
