I think the idea of the very high pressure 6.8 x 51mm round is to allow it to perform well in a 13" barrel of the MX5.

It makes you wonder if it's a limitation of the round, imagine the pressure generated if it was fired through a 21" inch barrel!

It's hard to see it having a civilian application too...

A few further observations on the MX5, it apparently has two gas settings, normal and " make it work" even its jammed with mud...

It somewhat surprisingly got a forward assist and one interesting feature are replacement sacriffical structural points, designed to do the 'stretching' instead of the upper receiver..... Interesting idea...