Currently the options are to use either thrid party cookie or first party cookie.
With third party cookie the visitor ID is in sync across domains, but third party cookie support is reduced over time.
With first party cookie the visitor ID is different on different domains, prohibiting correct analysis of unique visitors across multiple domains.
Solution:
Use first party cookie as default, but use a third party cookie to sync the cookie information across domains.
This way the main functionality is based on FPCs with all advantages. For all users who accept thrid party cookies the information are synced across all domains.
This could also be used to sync cookie information for cross visit pathing, getValOnce information, Timestamps for campaign expiry....
