Although the output of --list-packets should not be parsed and is subject to change with each versions we know that ppl do it anyway and things start to break.

It is indeed not a good idea to parse output subject to change at any time. This was not the intention behind the patch suggestion.

Thus such chnages will only be done when they are really needed. For all other the rule is still: Use the source, Luke.

This brings up the intention of the patch. I'm sure a lot of GnuPG users are not C programmers; the intention of the patch was to help such users better understand the output of --list-packets. ?

Even when we added lines starting with the usual comment sign (#) to indicate the offset of the packet, we received quite some bug reports.

The "#" lines are surely helpful; a non-programmer user can use metadata like this to orient themselves wrt the spec. The patch suggestion is in this spirit.