SEO of Location Meta Descriptions / Keywords

My view is that if you have more than one site i.e. have Addon Sites, the location meta description and keywords section kind of becomes redundant in terms of being able to utilise it.

So have been wondering for a while could something like ‘merge tags’ work?, i.e. have ‘merge tags’ (or similar) relating to each site and its main/sub categories.

As a result, could this be a way to encourage/assist search engines in picking up less generalised or misleading text in the search result?

Only a suggestion, as I’m not really sure if it's cost effectively feasible, or beneficial to the mass.