Next I installed libgl1-mesa-glx-lts-wily:i386, and indeed, now there's a replacement for it shown in the list:
$ hwe-support-status --show-replacements linux-image-generic-lts-xenial libgl1-mesa-glx-lts-xenial linux-generic-lts-xenial xserver-xorg-lts-xenial libgl1-mesa-glx-lts-xenial:i386
Next I installed libgl1- mesa-glx- lts-wily: i386, and indeed, now there's a replacement for it shown in the list:
$ hwe-support-status --show-replacements generic- lts-xenial libgl1- mesa-glx- lts-xenial linux-generic- lts-xenial xserver- xorg-lts- xenial libgl1- mesa-glx- lts-xenial: i386
linux-image-