Though the route you mention is also an argument against dramatic increase in ranges, there are three superchargers along the way. I put in 1.2X speed, payload 500 lb, and temp 35F. It came out to 162.5 KWh. You don't need a 800 KWh battery for that trip. It's doable with an existing 90 KWh. That's doable with one stop with a 120 KWh battery with plenty of reserve to spare.
A 500 mile rated range is around 150 KWh pack.
There are some gaps in the supercharger network today that would be bridgeable with a battery around 200 KWh. One example is I-80 through Wyoming. There are no SCs between Salt Lake City and Cheyenne. It's a stretch of 439 miles and the speed limit is 80 mph. Just driving the speed limit on a mildly warm day (80 F) requires 141 KWh. Just doable, but this is bridging one of the last supercharger deserts in the US SC system. It's likely this gap will have 2 superchargers in the next few years.
We can look at an Autobahn situation. I mapped out Berlin to Saltzbergen, Germany, which is just about cross country in Germany from east to west. It's 291 miles. At 1.5X the speed limit in EV Trip Planner, the driving time comes out to 3:08. It looks like they are using about 65 mph as the speed limit on Autobahns. 1.5X the speed limit is around 100 mph.
The energy used is 162.9 KWh. If you had a 150 KWh battery, you could easily make it with one supercharging stop. There are two superchargers along the route now and one at the destination. It's doable in an existing 90D driving 100 mph. With a 150 KWh battery, one short charging stop would get you the whole way. When temps go down, energy usage goes up, but usually 20 F temps also require slowing down too. 20F with 1X speed multiplier drops your energy usage to 120.2 KWh for the trip.
There will be some minor improvement from better energy density batteries, but the gains are not going to be that great. Improvements from weight savings and other improvements are only going to be incremental, a few percent here and there. The biggest savings will probably be when external mirrors are eliminated.
The biggest boosts to range are going to come from larger battery packs, but the 150 KWh is about the largest anyone will need until you get into some severe edge situations (like crossing the Australian Outback). All Tesla needs to do is erase the impression people have of EVs being short ranged. Once their top end cars have rated ranges up around the middle of the pack for ICEs, the cars will be capable of 99% of on road driving situations, even in bad weather, or marathon drives.
By the time we have the capability to make economical 150 KWh battery packs, the charger network will likely be much more extensive than it is today. I suspect that when and if it's ever offered, most people will go with a smaller battery pack because it will be cheaper and "good enough" for most road tripping situations. Only the marathoners who want to drive 1000 miles in a day or have Autobahns or really high speed limits are going to even consider a batter pack as large as 150 KWh. With a lot of smaller battery pack EVs on the road by that point, places that have high speed limits today might start dropping them.
