It would be great to have the option of previewing the app while building it on the web(App Builder interface). With the current setup, in order to see how the app works, one has to publish the app, select whether or not to send a notification about the publishing app, open Go Canvas app on mobile devices, re-sync and then at last test the app. The number of steps involved in this work flow is a huge time killer as well as require multi version app publishing when working on apps that have several screens, fields and logical conditions.
If we have a web preview in the app builder interface where we can click and visually see how the app looks and works on the mobile devices, make changes accordingly and then publish it. The time saved and the need to publish multiple versions of a same app will greatly reduced.