Typing tests and competitions are always derived from literature and non-fiction articles/summaries. How amazingly cool would it be to have a 1 to 5 minute test where you're typing out a program, script, or block of code? It would improve speed like anything else, but extensive use (perhaps in test styles like typeracer's or 10fastfingers's) would be better than drills at getting the student to develop writing logic intuitively.
Additionally, this could work with a Q&A design, similar to flashcards. With Linux commands, there could be a simple request, and you would type the command and options to complete it. There could be a feedback section, so if something is off or a second option is possible, it could be suggested then added to the list of acceptable answers. This would improve the students' knowledge of different possible solutions and motivate them to find more efficient ways of doing the same thing.
Nothing like this exists currently, so it could be a selling point for your site, which is already really well developed and maintained. Plus, it would keep students around longer since they'd have incentive to push themselves to a more advanced level. Suggestions could lead to new ideas on course development and modification.
You could structure it in multiple ways, too. For example, if each item is tagged by topic and those topics were grouped by subject, tests could unlock based on course/unit/lecture/exercise completion. That would mean some tests were available to the community since some courses are. Others, you'd have to be a member for. Or, you could have random commands or lines listed to parrot, introducing people to syntax patterns without context or explanation while testing them on typing speed in a more traditional manner.
Regardless of how much you feel someone would learn objectively from an activity like this, the less time you need to spend thinking about what to type, the more cycles your brain has to think about how or why. It's like having a conversation: dwelling on the words impedes effectively handling the subject and having response options thoroughly ingrained allows for more fluidity.
If this existed, I would literally live on your site 24 hours a day.