I use Dyneema on my four "alpine draws", but in my experience, they are the least versatile in an actual alpine environment where you may have to sling some big blocks to bail. Even bailing from a BFT can take a few.I left several atop the Duet buttress a few years back, as I didn't know about the fixed anchor at the top of Direct. You can't knot them, so it's Dyneema girth hitched together. No I don't carry a cordelette as I climb on doubles and don't need a power point set-up either.
Based on what I have read over the years about the likelyhood of a rappel back-up actually working, which is to say tests show most people won't let go of the back-up if they just lost control of the rappel, I'd say melting is a very real issue. I would disagree that it's "ideal" for slings, maybe good for quickdraws.
And what about the texture of Dyneema? When you get it it's slick as snot, after some use it roughs up, after a little more use it's time to retire it. Based on the answers here, I could see a scenario where someone's laying on the ground sayin' "damn, it worked last time".
For everything except those four alpine draws, and yes I think it is the best stopper draw, that being the sling you put on a stopper you want to stay put, I went back to Nylon, preferably knotted Mammut 11/16 which is da bomb in my opinion.
Would I escape a belay with a Dyneema sling in a pinch, yes, have to be quite the pinch though,as I keep three prussics somewhere with me ( one in chalkbag, one as chalkbag loop, one in pocket of gear sling) at all times. Would I use one to ascend a line, or as a rappel back-up, no.
If I had to guess DMM is talking about using a Dyneema sling to make a rap anchor without a ring, then pulling the rope through it, which I'd guess it's toast at that point. Indeed we are discouraged from even doing a second rappel from a nylon sling in that scenario, but I think it happens.
We don't all get stuff pro deal either, so I think there is an inclination to use and retain skinny slings past the date they should be retired due to both the cost and their limited uses other than as alpine draws. My knotted nylon on the other hand is cycled through a few times a season as I tune up rap anhors on duffer routes hither and yon. Like I said, they have a place, but I think it's limited.