My question in more details:
are peer-to-peer networks still a good strategy to get free publicity around your book, or for testing a minimum viable product? Or are there other ways, more efficient...
When I give talks about content monetization, someone usually asks about piracy protection.
There is no way to protect against piracy.
My suggestion is always monetize piracy. How exactly you do this depends on your product.
P2P content provision can be used in many ways to boost marketing traction.
Big difference between free publicity + MVP testing.
And, I suggest you use Meetup. I tend to do all my MVP testing giving free Meetup talks to live audiences.
The questions you get will help you refine your pitch/copy + maybe your product/service/info design.
You might clarify your question a bit, based on where you are in your book's lifecycle + also your book title + topic.
Likely other people will have great suggestions based on your specifics.
I don't see why it wouldn't still be applicable. Peer-to-peer file sharing has been increasing ~50% ever 5 years since 2008 (source: https://goo.gl/6WN6hU).
There are also now additional tools that you can simultaneously take advantage of. For instance, although e-book reader sales peaked in 2011, there is a huge amount of traffic on the Amazon kindle store. Many authors use Amazon's option to provide a free electronic sample of their book, which I know from personal experience works. I often download free samples and then end up purchasing the book.
This is a fun question — you might know that Tim Ferriss also tested this strategy out on one of his earlier books.
I'm going to answer your question in a roundabout way, but I still think it'll be helpful...
There's no one-size-fits-all marketing approach. We have multiple seven-figure businesses under our parent company, and even though our businesses are all related, different marketing channels work well for different types of products/businesses.
For example, one of our businesses (Sumo) makes a good percentage of revenue from content marketing. Another one of our businesses (AppSumo) has historically struggled to gain much traction with content marketing.
We have a philosophy at our businesses: Test out a new marketing channel every month, and look for ones that hit.
A month is a good amount of time to iterate a bit on the channel and see if it can work. If there's no traction, move on to the next one.
Generally speaking, to test a MVP, I've noticed it is very valuable to depend on word-of-mouth and going "viral", because typically it's not reasonable (or worth it) to spend big budgets on advertising on other more sophisticated channels.
One of the biggest wins we've seen recently is using partner giveaways to partner with some similar products and get cross-promotion. We've gotten leads ourselves for about $0.10 per lead (the cost is any products we wanted to buy, but you may have partners give you products for free).
Hope this helps, and good luck.