In Cupertino must be very fast, because just four days after the release of beta 3 we have here the beta 4 of iOS 11.1, tvOS 11.1 and watchOS 4.1. Everyone who belongs to Apple’s developer program can upgrade as if it were a stable version either.
iOS 11.1 will be the first major update of iOS 11, which will add new emojis and some features such as Apple Pay Cash that is already being tested by Apple’s own employees in the United States.
For now, we still have no trace of other important developments such as iMessage synchronization in the cloud or AirPlay 2, so we assume that they will come in versions later than iOS 11.1.
As for tvOS 11.1 and watchOS 4.1, there are no significant developments beyond stability and performance improvements. At the moment we do not know anything about the beta of macOS High Sierra 10.13.1 but it is normal: beta 3 came out the day before yesterday.
Remember that, as always, you are solely responsible for installing these betas. They are experimental versions, with failures and that can go slower than normal. We do not recommend installing them on the iOS devices you use on a daily basis.