Personally, I have a question. Who would want to do automatic updates on either themes or plugins? It is almost inevitable that there will always be a clash of something that will not always go well and end up in making a site inaccessible. This is the whole point of making sure that a site has its own version in a staging environment, the if all updates pass, push them out to the live site.

I understand that this may be useful for those who may not be as inclined to frequently check for updates to themes and plugins, however, I don't think it should be pushed as a mandate. As long as it provides an option to turn on or off, then fine. However, be sure to include a granular option to narrow it down to those item's that you are confident in with their updates to allow accordingly.