"I'm interested on what you (and anyone else) thinks about the opening tempo in the first movement in the Sixth....to me, it doesn't work, but it's certainly an interesting take".
I'm not bothered by the relatively slow tempo for the start of the symphony. In fact, I think it helps in making a strong contrast to the sweeping, lyrical second subject: the so-called Alma theme. What I am somewhat bothered by, is Chailly's refusal to speed up at the end of the first movement. However, Chailly may have Mahler on his side, as Mahler doesn't call for a big speed-up (I forget what he wrote, but I'll go look it up later). Since Chailly's scherzo is a bit on the slower, more lumbering side of the equation, it's probably a good thing that he didn't end the first movement with a super-fast tempo.
In summary, I would have liked just a slightly faster ending to the first movement, matched by a slightly faster tempo for the start of the scherzo. That would be more my ideal of how that transition should go. In fact, I've often toyed with the idea - just in my mind, that is - that the last note of the first movement should also be the first note of the scherzo. It would have to be a solo timpani note, obviously.