There might be some characteristics of the Lambdas that don't work well for the Minivan buyer - let's turn this positive and list them out...
So far, I've picked up from empowah:
wants:
lower floor/low step-in level
less bulky seats
smaller wheel wells
more cargo space behind 3rd row
flat floor
seats that can have stuff slid under them
sliding door
doorsill area by sliding door
replace center console with foldable tray - ensure access between front & back
butt-level seats
good view out front & sides
maximize space at expense of style
removable or fold-flat seats (which one = preference issue)
engine access in-cab or not in-cab, long hood vs short hood (preference issue)
flat load floor at the rear hatch opening (no step-down design.)
A split rear hatch, either like station wagons of old with a 1/2 glass opening window and a drop-down tail gate, or the Dutch-door concept of the Astros.
if featuring rear doors they should open 180 degrees, like an Express van.
Trailer towing capacity up to 5000 lbs.
AWD available
diesel engine option
Adequate lights, both inside and out, Xenon preferable.
Full instrumentation
Other than a basic AM/FM radio, other entertainment or electronics should be optional.
4-wheel disc brakes with 4-wheel ABS.
dual sliding doors
competitive price
Any additions from others? Let's turn this constructive, whether it be where the Lambdas fall short, or where a GM minivan could excel... heck, if you disagree with anything listed above, say so nicely, and we'll note it...
*edit* - added removable or fold-flat seats, hood stuff, buncha other stuff...