I/O support for more file formats. Ideally this should not add any hard requirements, but rather adapt itself to whichever combination of packages the user already has.
Add functioning Filters and EQs. This is challenging due to several reasons: 1. maths, 2. deciding on a good user interface (which filter designs should be included by default? how customizable should they be? how do we name the classes?), 3. efficiency of implementation, 4. enabling parametrization.
Extend parametrization to facilitate FM synthesis - we have all the necessary ingredients implemented, but currently this is only partially possible because they haven't all been linked together. This may require merging Signal with Curve.
Add and extend musical input methods.
Audio analysis and visualisation options.
Full support for wavetables.
More specific future features/fixes:
More fade curves
Expose Signal.from_ndarray method or something similar to give more options for easy Signal creation