You are welcome to contribute to DokuWiki and join the development.
What you want to contribute is of course up to you — you should scratch your own itches first. If you need some ideas of what is missing you should have a look at the bugtracker or on the idea pages. You could also consider adopting a plugin or template. Begin by reading the Getting Started chapter.
Working together is more fun. The DokuWiki community needs a lot of different skills and is organized in teams. Please feel free to join one or just hang around the mailinglist and irc channel for development talk. There are also regular IRC meetups, bughunting weekends where eh, bugs are fixed, and sometimes developers meet IRL at DokuWiki hackfest.
DokuWiki was a mentoring organization for 2011's Google Summer of Code. If you are interested in getting involved with DokuWiki development via this kind of initiative please contact us.