It’s actually been about for a couple of years but doesn’t seem to have gained much traction as a “standard”…
From a technical point of view it makes sense, bigger diameter bar means more clamping surface, more potential stiffness, but then 31.8 was already perfectly adequate, nobody was complaining about the need for stiffer bars really were they? Not that that seems to be a barrier for new “standards”…
I suspect the real reason it’s not taken over as the defacto bar/stem standard is that it doesn’t quite have the ‘SRAM blessing’ RF, syncros and a few of the finishing kit manufacturers might have pushed 35mm products out but unless SRAM tell all of their OEM customers that they WILL be getting 35mm truvativ OEM parts next year, it’s not going to take…
And of course the problem is that it’s maybe a little bit too backwards compatible for their liking, a couple of quid for a shim and any old bar will fit in those 35mm stems, if they can’t convince you that a new stem, means new bars I doubt they’ll force the issue…
But I bet there’s something else much “better” in the works for bars and stems, just you wait, you’ll all get settled on boost/tapered forks and they’ll change the upper steerer to a nice round “metric” 30mm, for which only special splined interface 38mm stems will be available and the corresponding bars will now have a larger diameter grip section say 24mm at which point you just say “**** it, nothing fits new bike time”… Or am I being cynical?