Reddit is most definitely not an "anti Redis" shop! If we were to rewrite it today, we might start with Redis. We've just put so much work into making memcached reliable and easy to understand for developers that the possible benefits of switching to Redis for many of these use cases don't outweigh the operational knowledge we have from years of running memcached at this scale.

That said - we use Redis in at least 2 (soon to be 3) capacities across the site for different services (outside of the monolith) and it works really well.