Q:

Expose the contents of the "accounts" tab of the SE network profile as machine-readable data

It would be really nice if there were a way to get all the data that is displayed on the accounts tab of the Stack Exchange network profile for a user (e.g. mine) as machine-readable data with a single request.   AFAIK, getting the badge counts requires making an API call to each site, so that getting the equivalent data for a user with accounts on n sites requires at least n+1 API calls. 

A:

As with suggested edits*, tag wikis, privileges, and so on... we don't expose things in the API until they've settled down quite a bit. 
Also, "Whole network" APIs are something that take a bit of work to get adequately performant.   A lot of effort went into getting the network profile pages to scale properly, similar effort will be needed on the API for those data sets. 
*Which are still not in the API. 

As of v2.0, the /users/{ids}/associated method (now consuming account_ids rather than association_guids) returns considerably more information (in the form of network_users).   This should be sufficient to mimic the accounts tab.