Ruby isn’t a direct Erlang competitor, and obviously, for intense low-level distributed concurrent work, Erlang is perfect. But if you have a project written entirely in Ruby, and you want to add Actor Model functionality to a small part of it, DRb/Rinda may be the best way to go. Even if they aren’t the best solution, there has got to be some way to implement solid concurrency in Ruby to optimize app modules.
Anyway, I think DRb and concurrent functionality will become more important to Ruby in the near future, and a Pragmatic take on this side of Ruby would be nice. Alternatively, a book could take a broader focus and describe “how to emulate Erlang-style concurrency in parts of your Ruby app”.
Or you could write an in-depth discussion about the actor model and how Ruby can use it to gain speed.
Just a couple of ideas.