See announcement here: https://media.pragprog.com/newsletters/2016-04-06.html
The plan is to do frequent updates tracking Rails 5.0 as Release candidates and the file release is made available, and to make updates based on comments made here in this forum and via errata: so please comment early and often!
One caution is that only https://rubygems.org/gems/rails/versions/5.0.0.beta3 is supported at the moment; the code in the book will NOT work with prior betas, and does not currently fully work with Rails master due to a regression that was reported and tracked as https://github.com/rails/rails/issues/23989
Phusion Passenger only supports WebSockets on nginx at the moment, the deployment chapter currently uses Apache http. I’m monitoring this, and may switch to nginx while the book is in beta.
Kaminari support for Rails 5 has not been released, though this only affects a single section in the plugins chapter. If that release is not forthcoming, Kaminari will be dropped from the book and I’m looking to find a suitable replacement. This issue was reported and traced as https://github.com/amatsuda/kaminari/issues/774
If you would like to try another version of Rails than 5.0.0.beta3, please check here for compatibility information: http://intertwingly.net/projects/dashboard.html before you proceed.
Note that the Rails team checks that page too before releases are made, so the book and Rails will remain in sync.
There are new changes in Rails master since beta3 was released that I’m watching: in particular there are setup and update scripts provided, and the rails restart command should soon work in development. Ubuntu 16.04 should be coming out in a few weeks, and the colors and book selection in the depot store may change before this book comes out of beta.