Getting back to the LVFS topic some years later now… 
In the meantime here is a thread about the same topic for the Librem 5:
In general, I don’t see much progress on this topic, however.
It would make updating firmware so much more convenient and even Dell XPS laptops support it, so you should really invest time in this IMHO! 
On the LVFS website it still says for Purism:
Testing is in progress, hopefully done soon! 2017-08-15
Has test account on the LVFS
Well… that’s not a lot of progress, is not it?
Especially since this was your last statement on this:
So, is there any update? This has obviously been requested for quite some time now…
And it would certainly make a great video, be it for the Librem 5 or any other device.
Note they now seem to have a nice dashboard for vendors and even consulting services are offered – should you need these.