The next major step for Facts is better charting support.
I'm currently planning to follow the Query/SearchEngine model, where charts are addressed by hash (so you can quickly edit/share them) and can optionally be named/saved.
I'm not yet entirely clear on how chart "types" will work. Essentially all current charts are based on time-series facts where it makes sense for the X-axis to be "time" and the Y-axis to be "value" (often "count"). At least for now, perhaps this is left to the API, but it would be good to develop a clearer picture of this.
Charts should also support a widget and maybe some kind of {chart XYZ} quick reference markup.
Continuity Across Axes: For functions that are continuous between discrete datapoints (like "accumulate(...)"), if there are points on either side of the domain limits (e.g., a point at x = -1 and a point at x = 1), we should interpolate a point on the axis. That is, here, if we draw only points in the domain, we get this:
We'd like something more like this, but without the glitchy rendering: