Actually, when my mom passed away I placed a quilt she had recently admired on the lower half of the casket with flowers on top (but that's because she loved flowers) in the 'viewing room'.
At the grave side service we had the quilt draped on the entire casket. It really added a bright spot on a bitter-sweet winter's day.
I think it's a great idea! Flowers really are too expensive! However, the living plants she received went home with relatives and two of the day lily plants became a part of the permanent 'greenery' on each side of the pulpit.