Basically there are three main steps you should take in order to adopt a plugin or template:
For authors giving their plugins/templates to adoption: use some tag? “orphan”? If possible send a mail to the mailinglist explaining which plugins/templates you are giving to adoption and in which state they are (and perhaps also some notes which skills the future author needs). Such a mail could of course also be used to find other people who are willing to help you developing the plugin/template.