> do I undertand mk/buildlink3/README correctly that _every_ package has
> to have USE_BUILDLINK3=yes, even if it had no need to use the older
> buildlink2? Eg, simple Perl packages would fit this description.

AFAIK yes, if you want support other installation types than "overwrite", 
but I might be wrong...

>   USE_BUILDLINK3=yes

Wouldn't it make sense to put

USE_BUILDLINK3?= yes

in bsd.pkg.defaults.mk ?

Cheers,
Marc