Not everybody is able or allowed to install another compiler or GUI library. Features should be present in all versions, or at least in as many as possible with a reasonable effort. Try to avoid that users must switch between platforms to accomplish their work efficiently. A patch for a new feature must include the documentation. Using examples is recommended.
Less documentation means that an item is easier to find.
Keep it small and fast. Vim can grow too, but no faster than computers are growing. Keep Vim usable on older systems. Startup time must be short. The time they consume must be as small as possible.