Thanks all for keeping me updated on developments in this area and new options.
Wakaku, great detailed post. What is Matroska HEADER vs XML tags as not sure I follow and Matroska spec is kind of confusing to try and understand fully.
Also discovered
MKV & MP4 Video Manager (MP4, MKV) - Not free, 25 EURO. I will need to start giving this one some tests and also looking at chapterEditor.
For those using chapterEditor does it cover most of the features of MetaX from perspective of MKV? I am pretty much using MKV primarily now.
Updated my original post in the begin of thread. Happy 2019!