I would like to thank everyone for the information, and don't worry,
I won't be doing this project myself :-)
Based on the good points made here, I won't be doing this on the door
to the laundry room because of the reduced clearance issue.
I decided, however, to do it on the closet door (93h X 45w). These are
currently quad-fold. The floor & ceiling is concrete.
Home Depot says if I want mirror these doors, it must have a track on
the bottom to support the weight. I spoke to my upstairs neighbor
(same layout), and she had her existing doors mirrored and she does not
have a bottom track (just the two pivot points on each side).
Thanks to all,
Clue-less in Philly