Well at the moment, I would consider Redis more useful than Varnish due to expired events. As to follow the "one caching model to rule them all" rule, how about using ngx_lua to dynamically change a static .html file with the data from Redis thus cutting out php-fpm (unless they are logged in, then requests will go directly to php-fpm)?

Or use Varnish, use Redis for expired events but with an empty value and use keyspace notifications to automatically remove the data related to that key from the database and purge Varnish.