I think t-spine mobility is important but, I think many drills that some coaches think are for the thoracic spine are limited by attempting to mobilize from the bottom up.
When we try to use the legs as "drivers" of t-spine mobility we are forced to go through the lumbar spine. This can mean many "bottom up" drills like hip crossovers, leg overs, Scorpions etc. can irritate an unstable lumbar spine in the attempt to mobilize the t-spine.
Top down techniques like the V-Stance T-Spine take the lumbar spine out of the equation.