Thanks! Cycling is on the to-do list. But I'm conscious it probably wouldn't just be a single category - there would need to be separation for road cycling and mountain biking.

The routing algorithm does already prefer roads with low speed limits, but there is definitely more that could be done in this space (e.g. a slider to set a preference to avoid higher speed roads). It also depends on the availability of speed limit data (I use the OpenStreetMap database).