Although according to your boot chart, you're not starting xinetd either ;)
Starting CUPS on demand isn't quite ideal sadly, if the user is using
network printers, then CUPS needs to have already been running for about
30s before they try and print otherwise the network printer won't be shown.
Sadly we can't "start CUPS 30s before the user needs it" ;)
Though I entirely agree in principle that CUPS is not part of the critical
path of the boot sequence, if the system is idle at some point, it's worth
starting -- even if that means the disk isn't entirely inactive after boot.
The most ideal way to deal with these kinds of services is to start them
after boot, when the system is idle - with low CPU and I/O scheduler
priority so that user activity takes precedence - or activate them on
demand by xinetd or D-Bus when the user actually needs them.
That way, if the user clicks print and cups wasn't running yet, it gets
brought up -- or if the user leaves their PC alone for a bit, we start cups
for the next time they click print.
Of course, even better would be if we could do network printer discovery
via other means like Avahi -- but then Avahi falls into the exact same
"start on idle or first demand, whichever is sooner" category