- Keep a per-application list of enabled addons and their versions (disabled/incompatible addons aren't interesting)
- If I install an addon on one machine, the other systems using the same application should prompt you to install that addon (ideally should just install it, but that's probably not super-awesome).
- We should figure out where to surface addons that the user doesn't install, so they can enable them later
- If updates are applied on one machine, we should apply those updates to other machines automatically, assuming compatibility (download, install, will apply without prompting on restart)
- If I uninstall an addon, we should uninstall it everywhere