Hello fellow porters! I wrote an utility called Panopticum [1] that uses Poudriere to build a given port with every possible OPTIONS setting, generate a packing list after each build and then combine multiple plists into a single one with necessary OPTIONS_SUB prepended.
It turned out to be far from a simple task due to possible cases like %%OPT1%%%%NOOPT2%%%%OPT3_OR_OPT4%%, but after cracking my head for a while it seems to work correctly now. The utility is already in the Ports tree under ports-mgmt/hs-panopticum directory. If you're interested, go ahead and try it out. I'll be happy if anyone finds it to be useful. [1] https://foss.heptapod.net/bsdutils/panopticum/
