My guess will be that if full glass panels, it might not be able
to hold the weight as the interchange is quite large in area,
unlike Serangoon, though my thoughts are the same as yours in the
usage of glass panel
Boon Lay Bus Interchange also not one hundred percent wall. The
walls at the bus bay can see through and look outside.
Joo Koon Bus Interchange same as Boon Lay, bus bay wall can see
through and look at the trucks and heavy vehicles at the warehouse
side of the building. The entire bus bay a bit similar to Clementi
Bus Interchange and Toa Payoh Bus Interchange: like a box flipped
to one side and one section is exposed to outside to enable light
to enter the bus bay.
Aiyah. Anyway, when the buildings are designed, the design has
to be reviewed by engineers, architects, BCA, .... before it can be
approved and the buildings can be constructed.
No worries. No need to over-think.
Just sit back, relax and enjoy the new bus
interchange. 
