went digging - 'cause Hendo has a reputation for being a generous guy,
SUFFERvision
watch the racing, and the watts, and see how 30" at 900 just gets the fast men primed for a nice kick.
sure, there are exceptions, but the positioning and tactics to pull this off at the WT level are not even feasible unless you have +900/50" power, at the end of a long hard race day. The sprint was about 10" long after Greg pulls off, and they were going faster than the leadout, so figure a few extra seconds on top of the sprint time, plus you'd need a harder launch that Henderson had when he went (+/-1200) so you could be clear...
sure, things happen and never-say-never, but as a legit tactic? Nah.
OP - HOWEVER - you aren't wrong that it seems like something people should try. Well, turns out they do. If you know what you are watching, you'll see guys try this fairly frequently, but it never looks like much because of how hard it is to move up near the head of affairs on a stage like this, then the power to launch, if you watch you'll see guys you don't recognize pop off the sides/front, jump across the road when the sprint trains are going - but it mostly doesn't register as a real thing because the lead out trains usually get them back in a couple seconds.
Even pros are out of fuel in a few seconds given how much is spent just getting to the front. Hitting clean air is a brutal realization that mortals just don't have enough.
Iljo Kiesse did a standing-start 1K in front of the pack a few years ago at the Tour of Turkey with only a few seconds gap and made it, but he's a freak talent at that sort of thing (you should also watch that highlight)
signed - a guy who can/has done this at lower levels, and knows the math all too well.
(Right echappy?)