Joni Mitchell is one of my favourite artists and Hissing Of Summer Lawns (and I've heard it in Quad!) is just brilliant I can play it at any time. It would be great to get the other Quads and possible 5.1 mixes too big an artist for D-V to get?
As far as the 5.1's, in the early 2000's there were a couple of upcoming release lists prepared by Warner Music that showed tons of upcoming titles that were never released. Included on those lists were Blue, Court & Spark, Hejira and Ladies Of The Canyon, which is the source. The lists seem to be pretty accurate because lots of the stuff on them came out years later (ie Talking Heads, Seal, etc.) so again it's entirely possible that that the 5.1 mixes are done, but there's been no confirmation of that either way. I would imagine that with Joni's current indeterminate medical condition it's probably night on impossible to get any of these released, but I'm entirely open to being proven wrong.
You never know if an album on a future release list was actually mixed - or just announced as planned. In the Quad Era - and again in the major label SACD/DVD-A days - a number of albums were planned and announced in Multichannel but then never remixed or released. Many reasons for that including the unavailability of the desired remix engineer and producer and artist sign-offs.
Well, 18 years on, we're still awaiting the 5.1 release of Hejira (and, uh, a few other announced titles). In the meantime, Rick Beato has broken down one of my favorite songs from that or any other Joni Mitchell album, "Amelia":