Lot's of potential things to add or change in the firmware, but I think the biggest one is 120 V charging behavior (no surprise to those of you who've seen my other posts on the matter).
As a great man once said, "Ye cainot change the laws of physics Jim!" (apologies to the butchered written accent), but even so there are some changes that could be made to make things work better for what is still the default shipped charging mechanism, and one that is talked about in the press every time charging is mentioned.
Basic issue with 120 V charging in case it's not generally known is that power is limited compared to higher voltage, higher amperage 240 V charging (thus the physics quote), and therefore Tesla does not have the car run any cooling cycle before, during, or after charging. The end result of this is that the battery pack is quite hot after charging. Hot enough so that it's pretty much guaranteed that the coolant pump will be triggered to run (and rear fan too, at times, at low speed). Given the heat mass and power drain of the coolant pump, it basically will never stop running and will drain the batteries down low enough to need charging again, keeping the pack hot and starting the cycle over again.
Two main options:
1) Raise the temp at which the coolant pump is triggered to run: Tesla seems focused on this potential "fix" and it'd be nice, if they can determine it doesn't affect safety or battery life. If this workaround happens, then the battery staying fairly hot all the time wouldn't get the never-ending cycle started... maybe. Regardless would be nice to have the pump run less *if* the pack balance and conditioning issues are ok.
2) Add in a cooling phase to 120V. There's not enough power (it has been said) to run cooling at same time as actual charging, but I'm hopeful that it could be done as a separate phase triggered by pack temperature or by charge progress state. Either would work so long as the pack ended with its temperature below the trigger point for the coolant pump.
There have been suggestions of adding in a compressor driven cooling phase independent of charging to help in high ambient conditions when the car is parked after driving. I don't know if that would be a win or not, but am pretty sure either or both of the above two would be big wins in the overall effectiveness of 120V charging.