I think what we're going to end up seeing is Model S features now will become Model 3 features, while the Model S will get new, better features. For instance, the center screen is only a 1080p screen. Every other decent screen on the market is 4K/Retina: iPads, iPhones, Samsung devices, laptops, etc. The Model S/X will probably get a high res, high contrast display in the not so distant future, and to save on costs, the 3 will get what the S has currently. The Model S/X will probably be a few years ahead of the 3 all along, as both a testing ground and premium experience. I wouldn't expect the 3 to have anything better than the S/X have right now.
I'd also wager (but I hope I'm wrong) that Ludicrous will not be available to even the highest end Model 3. We'll probably get a performance model with Insane, but they'll probably want you to move up to a S/X for Ludicrous. They have to have something other than size to keep people buying those. We'll also probably see the S/X get a 100+ kWh battery pack at the same time the 3 comes out with an 85. Again, to give the S/X a premium edge over the 3.
All I really want is 0-60 in ~3.5 seconds, autopilot 2.0, 250+ mile range and head turning looks. I'll pay what a 70 costs if they do Ludicrous.