This is where we're at at the moment:

As far as statistics tags go, BPS has been around forever but until now has seen little to no use, it will be joined by the new tags 'DURATION', 'NUMBER_OF_FRAMES' and 'NUMBER_OF_BYTES'.

There are two new tags added _STATISTICS_WRITING_APP and _STATISTICS_WRITING_DATE_UTC for programs to compare with the Segment Header's 'Writing Application' and 'Writing Date' fields to check if the statistics are valid for the current file.

It's at best a hack job, but the objective at the moment is to get these things working in a reliable manner without needing to add new header elements which may play havoc with existing software... again...

At the moment Mosu is considering adding another tag that contains the names of all the tags that the _STATISTICS_WRITING_APP and _STATISTICS_WRITING_DATE_UTC tags validate, so the process would be to first check the _STATISTICS_WRITING_APP and _STATISTICS_WRITING_DATE_UTC with the Segment Header, then check the known statistics tags with the list of validated ones and only then use those tags that pass as actual file statistics. The current solution is kind of like playing with batch, but despite having had a BPS and other stream Tags since inception the Matroska Tagging System just doesn't seem to be set up to actually use the things in a real world environment.

Mosu isn't interested in encrypting the tags or adding a prefix to the Statistics Tags' names. If anyone has a better idea on how to achieve this objective without mangling the file suggestions are welcome.

Mike from MakeMKV has shown interest in these file statistics tags, Jerome from MediaInfo seems quite happy with them and there's been at least one other major player in the encoding community paying close attention to proceedings. I'm probably not the best ambassador for... well, anything, but apparently I'm caught up in this.

(Of course, MKVMerge will include an option to disable the generation of these tags for those who need it)