The formula for constant acceleration is v = 2 * d/t - final velocity is twice the average
I can agree with v = d/t yielding average velocity.
However acceleration during a jet takeoff is not constant as thrust from a jet increases non linearly as speed increases. Drag generally does not offset thrust increase while on the runway during takeoff.
As for shadow angle from the wing, corrections could be applied for earth rotation and latitude-longitude change as well as wing flex. Note that on the runway the sun is lined up close to the wing axis. The wing tip shadow stays in a constant relative position to the outer flap canoe until liftoff. A beer says any correction would be less than 10 cm. Etkin in
Dynamics of Atmospheric Flight states that earth rotation and latitude-longitude change effects are negligible until in high mach flight.
Like the original poster I have had a similar view of the opposite end piano keys departing on a hot day and still wonder how things would have turned out had we had a V1 cut.