Hi Jim. For me, at least, the thing that makes this topic interesting isn't a concern about water coming through the tent or otherwise dripping/pouring into the sleeping bag down from the outside. It is, rather, the combination of humidity and of the moisture given off by the body during sleep. That, combined with multiple day trips.

For an overnight or "couple of nights" trip, loss of loft isn't generally a concern. But hike in conditions where it's very humid out and no matter how good your DWR treatment, the down in the bag can get ever more damp each day with a concomitant loss of loft --- and thus warmth. Barring a fortunate break in the weather, the only way to re-loft the bag at that point is to go home and dry out!

This is IMO an even bigger topic the colder the conditions. I've (happily) never used a vapor barrier liner in a sleeping bag, but that what it's about, because loss of loft is deadly serious stuff in colder winter conditions. So I would think that down that does a better job at retaining loft in moist conditions would be of even more interest for winter/very-cold use.

I guess we each see a new product like this from different perspectives depending on the particular issues we're concerned about. An adequate seam sealed tent and/or DWR on sleeping bag and/or decent light drybag to carry it in --- these have never been significant issues for me at least.