No open source project thrives on the work of one person. TurboGears is lucky, because we've got the help of everyone using the included projects. But, there's plenty we can do ourselves to make creating webapps easier and faster.
It should be just about as easy to contribute to TurboGears as it is to use. To learn more about getting code into TurboGears, you can take a look at the Contributing to TurboGears document.
The best designed APIs are the ones that are actively used. Growth in TurboGears should generally come from people solving real problems and putting in solutions to real problems rather than meeting some future anticipated need.
If you find yourself with some time and interest, there are some identified real needs in the TurboGears Trac. Because it is sometimes difficult to make heads or tails of a long list of things in an issue tracker, this page is a good place to come to see which things need help.