Major progress was made. Manged to get Anbox working in Whonix 15 (Debian buster based). I have a “proof of concept” on my local disk.
Comes with a caveat (Whonix-Workstation firewall needs to be disabled). This is already documented and rationale added as footnote.
Instructions might work but I didn’t test yet if they actually do. See footnotes for steps which may or may not be required. Help getting it tested and fully documented welcome.