I can see how having the command airspeed bug set at V2+10 would provide an airspeed target after liftoff (probably a more reliable target than the FD), but this would require you to make a mental calculation of V2 if you had an engine out.
On a normal
all engine liftoff Boeing recommend a rotation rate ( around 3 degrees / sec on most types )to an initial Pitch attitude. This will give you an initial speed of between V2+15 to V2+25. This speed
should be held until cleaning up the A/C. Also the Pitch Flight Directors
cannot be used from liftoff until the mode changes
from TOGA/TOGA
to THR REF/VNAV SPD at 400', at this time they command your current speed ( within V2 to V2+25 limits)
If you suffer an Engine Failure on or before rotate then a slightly slower rotation rate to the recommended Pitch attitude ( 2 to 3 degrees less than normal ) should give you V2 to V2+15. ( V2 absolute minimum ) once again hold this speed until 400' and THR REF/VNAV SPD then the Flight Directors will command your current speed ( within V2 to V2+15 limits ) until cleanup.
The Bug
should not be set to anything but V2 and I know that Boeing would not agree to any Airline changing their procedure in this respect.
I agree, but airlines still do modify procedures.
They do under Boeing and Airbus's ok, but not in this case.
CX, KA, QF, BA, NZ, MH, SQ, JA, etc etc ALL set V2.
It's not rocket science.