BSDs (and some others) come with variously-named Handbooks. OpenBSD has the aforementioned. FreeBSD has a Handbook. So do DragonFly BSD, NetBSD, and others. They are distinct from the user manuals, which are the reference doco. They are, indeed, hyperlinked. Already.
* OpenBSD FAQ: http://openbsd.org/faq/index.html
* NetBSD Guide: https://netbsd.org/docs/guide/en/
* FreeBSD Handbook: https://freebsd.org/doc/handbook/book.html
* DragonFly BSD Handbook: https://www.dragonflybsd.org/docs/handbook/
* GhostBSD Handbook: https://wiki.ghostbsd.org/index.php/GhostBSD_User_Handbook
* MicroBSD Handbook: http://damnsmallbsd.org/MicroBSD/handbook/
* OpenIndiana Hipster Handbook: http://docs.openindiana.org/handbook/getting-started/
* old TrueOS User Guide: https://trueos.org/handbook/trueos.html
EDIT: i see some of those are authored in DocBook but still info files can in theory be written in DocBook too. The main focus of my comments here is the end user format and viewer capabilities, not the authoring format (and honestly i'm not a big fan of info format with its hardcoded text formatting).
Note that this isn't about it being technically impossible, you can certainly do it, but it isn't the right tool for the job - a dedicated manual reader provides a better UX here (and the failure of GNU info to provide a user friendly experience is, IMO, the reason manpages are abused so much in Linux).