Hi,
Maybe you could think of a Global Edit Counter page with only global info, like all accounts (from Special:CentralAuth or from sulinfo, the second is better because there is creation date and not attach date), and statistics (yearly, and monthly if someone has EditCounterGlobalOptIn.js, time card maybe also) summed from all wikis with colors assigned to wikis (instead of namespaces). Latest global edits would naturally belong there, and on existing Edit Counter pages there could be only latest local edits.
Regards,
Mik.