That "little thing" which maintains and generates the timeline should be IO bound whether it's written in C or Ruby unless it's written by someone who does not understand the problem space, and ought to be a separate service. We can agree Rails doesn't make much sense for it, but frankly, language does not matter. Understanding how to minimise context switches for a network service and how handle fan-out does. It's not a hard problem - it's been solved dozens of times over by people writing queueing message servers, NNTP servers and SMTP servers, amongst others.