For info the outfit that I am familiar with uses reduced thrust / flex takeoffs wherever possible and I think that most outfits do. In lay terms this uses an "assumed temperature" method of calculating thrust that "fools the aeroplane" into thinking that it is weight limited due to ambient temp.
Hence the aircraft always rotates at about the same distance from the end regardless of weight. (Sounds funny until you think about it / less weight - less thrust).
Following on from this the length of the trend vector is always roughly about the same - regardless of weight. In the particular aircraft I am familiar with it is about "25 - 30 kts in length". The only time it varies is on a light weight/high thrust takeoff - unusual but possible due to contamination or MEL requirements etc. In this case the thrust vector is longer. So a simple "gross error" check can be made very early in the takeoff roll - like just after thrust is fully set.
In my aircraft, if the length of the trend vector is less than 25 - 30 kts - stop! It can be done so early in the takeoff roll that the stop is quite gentle - i.e not a passenger screaming abort at high speed. As I'm sure most drivers are aware the trend vector is a fabulous indicator of wind shear on the runway and I am a big believer of the PM being "trend vector aware" during the takeoff roll.
Following the Auckland accident I tried setting up the FMC (in the Sim) with the ZFW set as the TOW and believe me the trend vector was really short - like about 5 - 10 kts. Unforunately the heavies in our airline didn't want to consider introducing the idea of trend vector monitoring by the PM as standard. They did concede however that it was acceptable as an "individual airmanship check".
Interested in whether other use this or considered views.