I noticed that most of the time spent starting QNX actually goes into device detection, so I started wondering how to supply sysinit with the list of hardware on my platform (in this case, an ancient-ish laptop)? /etc/rc.d/rc.devices and /etc/system/enum/* apparently need some trimming, but what exactly?
After your system booted, open a pterm window and enter: ‘pidin ar’. Here you will find a list of resource managers started. Use this list (and their parameters) to create your own sysinit. The manual will guide you. If I am not mistaking, there is a chapter about the QNX boot process. Read it and build your own sysinit. Be aware that sysinit is the first file that is called by .boot or .altboot.
Hopefully this will help you out. If you run into issues, let us know.