Adding dashboards to hledger

I spent a couple of days trying to hack some changes into hledger-web. I use it from time to time, especially to visualize the item tree generated from my journal, but I would need more to incorporate it in my workflow. What I would like is a system to describe arbitrary widgets to compose in a dashboard. Things like "monthly expenses, comparing this and last year, using a histogram". Or "breakdown of the top N expense categories, using a pie chart".

So far, I just built some familiarity with the codebase and I managed to obtain a static (I mean, non-configurable) dashboard with a single widget showing my monthly expenses. Like that (code is on github):

But the real problem is designing a sensible dashboard configuration language.