The dual motor cars are not as rear-biased as they were last winter. I looked at ScanMyTesla while driving on snow and ice. Once the car detects slipping at the back, it starts using the front motor more than before. It gets used in regen and in acceleration, even in gentle actions (as opposed to just in hard acceleration like before). Eventually if the car doesn't detect slipping for a little while it will revert to a rear bias for efficiency.
As for the back sliding under regen... the only way for the software to find the traction limit is to go over the limit. Therefore, the tires will lock for a fraction of a second. Regen will lower quickly and the stability system will take over and ensure you don't spin out but you need to get used to it. The car will constantly try to raise the regen so it will hit that limit again. It's the only way to constantly be around the traction limit.
The car is still very "careful", preferring to brake all the time when trying to corner. It has a very understeering behavior which I don't personally like, but might feel safer for others.
"Slip Start" behavior also seems to have changed. This year it allows a bit more rotation of the car. Instead of just lowering the traction control activity, it seems to relax stability control a bit. I prefer to drive on snow and ice using that mode. Now, this might not be good for people that already feel nervous of the back slipping under normal conditions because of regen.
Starting off heavily rear-biased and waiting to react to slip that already happened...
is rear-biased. If the car remembers that slippage for a bit then automatically tried a heavily rear bias again, that sounds unpredictable to me as the driver, and doesn't really solve the issue (even if it helps some).
Let me be frank: If maximum traction in snow and ice is your goal, reactive AWD just isn't as good as fulltime AWD.
You don't need to find the traction limits of each wheel to understand that most likely the front wheels have
some traction, and using only/mostly the rear motor initially for acceleration or regen is almost always going to make slipping and spinning easier than starting off around 50/50. Again, normally what the Model 3 does is fine and good (I like how it drives!), but it should be easier to force a more balanced torque distribution. Probably all we need is the Model Y's "Off-Road Assist" mode.
I've driven ICE cars with essentially reactive systems not unlike the Model 3's normal behavior. They have a clutch-based center coupler but no actual center differential. They have the same tradeoffs as we do: They retain much of the driving feel of their base RWD or FWD roots, they're more efficient than fulltime AWD, they do have lots more traction than 2WD...but their behavior in slippery conditions just isn't as good as fulltime AWD.
Our cars
could do much better than those part-time AWD ICE cars, because our cars
could proactively drive both motors without the downsides of those crappy (IMO
) center clutch coupler AWD systems. M3P and MY already can! (Track Mode and Off-Road Assist, respectively.) And of course our cars will immediately drive both motors when you request more torque than the rear alone can deliver, but that's going to be way too much for the snow.