You probably need some inside contacts with the registrars for the site you propose. Generally extensive use of the whois databases requires some financial arrangement, as in paying for it I believe. There is a lot of competition in this as well, and many places to get expiring domain info for free or relatively cheap. Whois.sc is one such service.
Another possible use with less competition would be for domain owners to get an alert when Their domains are coming up for expire. Fabulous.com offers this service to large users, but I haven't seen much other competition. This could be a backup if whois email changes, email gets lost, or just to consolidate info from multiple registrars in one place. It may be easier to get this type of registry connection as well since it probaby isn't as resource intense.
Good luck.