I would expect some type of price decrease by 2021. Probably like SR+ starting at $36,000 and AWD LR starting at $42,000 or something. That gives a little room to slot the Model Y in above those by $1,000 or $1,500 and then still have a little room between the truck. I figure base battery will be 300 mi on the SR and 400 mi on the AWD with possibly a 500 mi option on the AWD or standard with the Performance model (if it can fit). I suspect Model Y specs will fall in line too with that and price will be adjusted some. I doubt we'll see air suspension and stuff like that showing up on the car. That really does seem to be a utility for the truck (probably the only way to get that kind of efficiency while also allowing for a 16" ground clearance and then of course the side benefit of having access to compressed air). I doubt we'll see any other major feature upgrades to the model 3/Y. I wouldn't be surprised if power stayed about the same, or a few horsepower above whatever else is on the market at the same range and price point. I figure SR will hover around 300 to 325hp and LR AWD will be 415 to 425hp.
I really think the major factors for the 3 and Y will be range and price. Obviously it looks like Tesla is working on a pretty large upgrade to battery cells or packs if both roadster and the truck have 500 mile range options. Roadster doesn't look THAT much larger then a 3 (and might actually be smaller) and the truck has got to be more on the order of X weight. So I wouldn't be surprised if 3/Y ended up with 75kWh, ~110kWh, and 150kWh. That seems to scale fairly well with the current range differences with 3. This would be a massive improvement for them if they could get it in the same physical package, but to me is the likely evolution for those two models.
I think a 300 mile range is probably as much range as anyone needs when having access to daily charging (at home or at work). This still allows good road trip ability and pretty good penetration into remote areas like coastlines or national parks/winter retreats that might not have superchargers in a linear point to point configuration. (Meaning you need to take enough power with you to get into the remote area and then back out to the supercharger before heading home) Charging to 75% would give roughly 200 real world highway speed miles which means you're good for about 75 miles into a forest/mountain and then back out with some buffer for elevation or comfort. That'll cover a huge amount of cases around the US and then continues to get better as superchargers come online.
I think 400 mile range probably is going to be what lets non-daily charging people comfortably feel like they have a "normal" car. At 85% you're getting 340 miles, which works out to about 60 or so miles a day for the work drive and running the kids to school or something. Then you swing by a supercharger on Friday night while you do some shopping or go out to eat or whatever, and you're charged up again. You've got a buffer of about 20 to 30 miles to burn on the weekend. If you're only driving ~30 miles a day during the week, then you can charge to a lower SOC to reduce the charge time and be more gentle on the battery, or shift some more miles to the weekend (say 150 miles). The 20 to 30 mile daily driving would work well for this model in colder areas. Either way, a 400 mile rated battery really opens up a family that then relies on a supercharger for every 4 to 7 day charging and mimics the gas model fairly well. (if you're charging every four days maybe it's a 20 minute stop, if every seven days, maybe it's an hour while you're buying groceries, etc)