Moped 2 supports a pool_timeout option. But when I tried adding this configuration option to my mongoid.yml (Mongoid 4.0.0), I got the following error message:

Optionable::Unknown: :pool_timeout is an unknown option. Valid options are: :write, :read, :database, :max_retries, :pool_size, :retry_interval, :refresh_interval, :down_interval, :ssl, :timeout, :instrumenter, :auto_discover.