Other than digging though Github, is there a public roadmap for new features and such for Frappe/ERPNext?
I like to develop new features via my own custom apps, and sometimes patch different bugs that I find, but sometimes I find myself wasting time because those things are often already under development, anway.
Nope. This is deliberate. Frappe development is much less centrally directed than in many other projects. As I have understood it, architectural changes are discussed and implemented by the maintainers internally, but feature development tends to happen whenever somebody with the ability or resources feels motivated to make them happen.