Maybe this is obvious, but I agree with the notion that the 4680 pack will probably NOT substantially add to range. Tesla will take additional profits and recognize weight savings from being able to put in a smaller pack for the same level of energy density. They have also hinted that they will use the weight savings to add extras like air suspension, a luggage cover, revised seats (cooled maybe) etc. I feel like Tesla really needs to do these things, as they are still a small automaker compared to the big boys and anything they can add to stave off the likes of Ford, GM, Xpeng, etc is going to be needed to keep their #1 position in the world of EVs. As others said here, most of the advantages of the Austin cars is going to be in manufacturing simplicity and lean advantages to enable Tesla to make cars faster and of higher quality fit and finish. The outward appearance and actual performance of the cars, IMHO, will not change much if at all.
The other thing here is that - at least in my experience - my Model Y Performance and several friends' Model 3 Y S, etc, have NEVER been able to reach the full range stated by the EPA. For example, 303 is my stated range but when I brought my car home brand new it only ever was able to charge to about ~280 miles. Yes, some of this is just standard BMS math/trickery, but now after 7K miles and very conservative charging, my Model Y can only charge to 265 miles at 100%. It's not my imagination either - the BMS is reporting correctly from what I can tell. So, *maybe it's possible* that the 4680s having the advantages they do will make these cars actually go the range they have always been stated to go, not more. Plus, then they might be in a position to UNDER state the range which is never a bad thing for ongoing customer satisfaction.
My 2c,
J