This is a great improvement, and having JSON data for the metrics means that you can skip having the server render all those graphs via rrdtool and instead use something like HighCharts or other Canvas based graphing toolkits.
Now they just need to switch away from RRD as the backing data store. Until then I'll be looking at OpenTSDB/Graphite for a more modern approach to metric storage.
Graphite's whisper engine is very much like RRD. OpenTSDB on the other hand is not trivial to set up or manage. It all depends on your requirements and resources.