Since the release of the book, there have been hundreds of additions to the Linux fortunes (mostly from backdated posts I found on a number of gaming forums, but also from other places including a 2014 Buzzfeed article) as well as dozens of missed duplicates and near-duplicates removed. As of February 2019, there are 6850 (6712 plus an optional "offensive" set of 145) total Linux fortunes, while the 2017 v6 book contained 6596 YKYWTMSMWs (Mara's 2007 v5 book contained 6045).
As for the when the next version of the book will be put together, it will likely be the earlier of these two events, rounded to an important date like a Senshi's birthday (I released v6 on Ami's birthday):
A few months after the second half of Stars and the final Crystal movie have both been released in the US on Bluray/DVD by Viz. I'm guessing all of this will happen by the end of 2020?
A few months after the next stable version of Slackware Linux is released. Why Slackware and its next version are relevant here is too TL;DR for an anime forum. Slackware releases new versions extremely randomly, with its most recent release v14.2 being in 2016, with the previous version v14.1 released in 2013, and v14.0 released in 2012.