All of the above. Some ware based on real hacks. Some are made up to facilitate common exploits. Some ware made hard with what at the time was fairly unknown. Some started off as a list of real exploits(ever notice that the irc ones aren't sequential? that is because 2 of them on my list ware too tricky for me to actually implement)
There will in the future be new stuff, but considering the nature of the site its often difficult to find good staff to write them.(people are unpayed, easily distracted and lazy)
Users are of course welcome to create missions themselves. After running a beta of it on the forum it could be included in the rest of the site.
There are some ideas floating around, but turning them into reality isn't always easy.
If anyone here is sufficiently good at ipfw/pf settings (nat, reverse nat, setting+cleanup scripts, on a multiple ip setup) feel free to PM me if you want to be put to work