Best practice for informing users of upcoming features

We are currently in the private beta stage of an Agile project delivering an internally facing information application for a client. This is a replacement for a much older legacy system which is feature rich, but has a multitude of UX problems.

In the run up to private beta we put a huge amount of effort into our comms to try and ensure that users understood the Agile process and concepts such as MVP (at a very high level). This was to ensure they didn't think that we were taking things away, just releasing them incrementally.

However due to a muddled comms structure within the organisation we have perhaps not had the penetration we would have liked.

As a result we frequently get users who give feedback asking for features which are still in development. This is to be expected of course as to them all they see is that something isn't there that they used to have.

However I would like to know if anyone has any experience of informing users of upcoming features and how they went about this ? Obviously there are issues about making a rod for your own back by being too specific for example and i'm sure there are others !

I've seen lots of information on 'New features' but not necessarily 'Upcoming ones'.