In my opinion your burning leaves smell would be picked up by the Grove Dust sensor. I think the sensor which has the best chance of picking up the Garbage smell (out of the sensors we are using in this IAQ shield) would be the Figaro TGS2602 hydrogen sulfide sensor.
I have not yet played with any of the shields precise components yet, but I have a dust sensor and it does go high from smoke. I have a formaldehyde detector and I know when that gets high readings. I had a professional CO detector a few years ago.
I still hope that Spark will produce a run of these shields, but I expect it will come down to the number of people expressing interest in them. Also, I dont think the run will be imminent, I think Spark are busy with office moves and the recent funding