Hi Remi, thanks for your words and really looking forward having you on board for the next books!
I am really committed with this group and feel in charge of leading somehow. Sometimes, I start the book only 2 days before the debrief session and spend part of my night reading in order to finish it before the deadline.
To be honest with you, it is very hard to read additional books since we started this book club as I also belong to the actionable book club for which I read and summarize books too (1 per month), excepted during the holiday (and I can read in french by the way).
We do not really focus on specific topics. If you take a look on our book list, you can see that all books are classified by topics. There are multiple. Everybody can add any book in the list and the group votes.
A good way to widen our horizon is to share a common project. By writing a book with Josh and Beverly, we widen it and it forces us to look for different and new topics and go further out of our comfort zone (trust me, writing a book is realy out of my comfort zone at the moment).
Hope this will answer some of your questions.