Stilton,
I thought JT covered your para 2 & 3.
Q: But what if you encounter a major wind shear while you’re still trundling down
the runway ?
A: you reject the t/o and that shouldn't be a problem as your new "W/Shear" V1 is still within the performance limits of the a/c.
"If it’s significant enough you could be in a
situation where you don’t have enough
airspeed to lift off but your groundspeed
is too high to stop if you unwisely chose
to attempt to"
How so? If you encounter w/shear on the t/o prior to V1 your rejection should solve the problem, unless the shear has affected acceleration and you've not picked this up thus resulting in an overrun.
"I’d rather be in the air (where aircraft are
meant to be) with speed and some altitude
and go straight into the windshear recovery
maneuver, your odds are better"
Not sure about that! Plenty of w/shear accident history shows you may not be able to outclimb it. If you rejected close to V1 and overrun the runway I'd say there'd be less loss of life than getting airborne and hitting the ground some kms from the airport.
But, as someone earlier said if there's already been reports of w/shear best choice is to delay departure. Let others be the pioneers if they wish!