So far, the mattress has not expanded, especially the coils.  Right now it is not fit to sleep on.
UPDATE (4 weeks later).  Mattress did not fully expand, especially in the corners and on the ends where the height was about 8-9 inches max.  You can see in the pictures right side is higher than left side.  The sides seemed to bulge outward rather than expanding upward.  Further, the mattress maintained a curve across the middle from where it was folded and compressed for shipping.  It was very uncomfortable to sleep on, causing back, hip, and shoulder pain.  I cannot recommend the mattress, but Wayfair honored the 100-day satisfaction guarantee, sent a courier to retrieve the mattress, and provided a prompt refund.  So my rating is, mattress 1 star, Wayfair service 10 stars.