I took a similar model with Isomer: http://jdan.github.io/isomer. I tried it as an experiment, and was delightfully surprised by the number of people who wanted to pay for it.
So I guess for the author, without the Mac App Store, there's no hope for commercial success?
I thought the Mac App Store might take longer to gain full traction - the buy-and-download from the developer website model was pretty prevalent. I guess it happened faster than I expected.
The following app behaviors are incompatible with App Sandbox:
[...]
Use of accessibility APIs in assistive apps
With App Sandbox, you can and should enable your app for accessibility, as described in Accessibility Overview for OS X. However, you cannot sandbox an assistive app such as a screen reader, and you cannot sandbox an app that controls another app.