I recall at Laguna Seca 2006 when Valentino was forced to slow due to ailing grip. The ambient temperature was over 100F and the track temperature was something ridiculous like 140F. The cooling failed and the M1 spectacularly blew as he crested turn 2. I was outfied at Andretti and captured it on camcorder, and it looked identical to yesterday. The dirty air theory is plausible were it not for the fact as has been pointed out that it was about 66F when Lorenzo's engine let go. Ambient race temp was only about 78F so this shouldn't have been particularly problematic even given that Rossi was in Lorenzo's tailpipe so I agree that it is unlikely to do with overheating.
They will already have diagnosed the fragile top end and have solution ready to effect but as Pov quite rightly observes, I think it unlikely that HRC, given the inherent problems with their own motor will give their blessing.
Thinking about this, I recalled another M1 self destruct job - again at Sachsenring in addition to Nicky's RCV212 mash up. Can't recall the year but it was Lorenzo, and it was an ugly bottom end dump as I recall.
Worth watching this again. I hope Sykes had to pay for the additional damage he caused...
I love the way he detonates the casing.