Bandwidth Concerns - Enforce Playback Quality

Currently, only a user can enforce their playback settings for a given video playback instance.

I would like to understand your scenario a bit better to make sure I understand what exactly you are looking for.  With Microsoft Stream, we do adaptive bitrate streaming which, in general, creates mutliple bitrates. Adaptive bitrate streaming generally is used to reduce the amount of buffering experienced by the client, while still reaching the best possible viewing experience.  Additionally, the bitrate selected is a combination of video player size and available bandwidth.  What this generally means is on the video playback page, you will generally have 720p streaming, unless users are in full screen mode or using a 4K monitor which would be around 1080p - and this is most likely your average bandwidth anyways.   

In order to save network bandwidth, you would not want video streaming to occur in 1080p? Or would you like to constantly force the bandwidth at 720p, because that would potentially cause negative affects to those who do not have enough bandwidth to stream at 720p - I assume your more looking for a max bitrate of 720p rather than a default value?  In both cases, would not encoding the video to include a 1080p version fix the issue?  What a about a lower quality encoding profile which your could set at the administrator level work?