Many packages need keywording for ppc-macos support, and often I have to repeat the ekeyword command 5-10 times, for each dependent package, in order to get an emerge to proceed. This is particularly true of Perl modules, which have many dependencies, and typically work fine on the various architectures.
Very tedious! And all that work is gone after an emerge sync (I know, we're updating the packages as soon as we can report success... but in the development phase things are tedious.)
1) An option to apply the requested keyword to all dependent packages ( --deps)
2) By default, this option would prompt for each package; another option (--force) could turn off prompting, after dire exhortations regarding the madness of such an option
Sorry, ekeyword is much simpler than this request implies. It knows nothing of ebuilds, dependencies, etc. The functionality you're requesting would be better suited to another script that calls ekeyword.
Regarding emerge sync removing keywords, that's the point of PORTDIR_OVERLAY in /etc/make.conf