OK, warning this is going to be a bit long, also is personal viewpoint from someone who craves and appreciates change and advancement. I realize others can (and do) feel differently.
Exec Summary: Model S UI, though unconventional and with a few significant flaws, is tons better than other cars, and already "spaceship like" IMO. If Model 3 UI evolves that (whether it has additional readouts, HUD, or just tablet display), it will also be tons better than most other cars, and probably even more "spaceship like". It will just be different, and will require a bit of time to get used to.
Because we are migratory - living in several places, I had to choose to keep my P85 somewhere (vs. drive it back and forth thousands of miles). So, I get to alternate between Tesla and VW eGolf at one house, and BMW X1 and Mini at the other. Also, prior to Tesla, I had a Jag XF and previously BMW 5. So, I've lived with a few auto UIs. I say "lived with", because I do not think you can judge an auto UI without living with it... just riding in it or driving occasionally (e.g., rental) does not give you time to acclimate. Now, I have not "lived with" late model Lexus, MB, or Audi UIs. And I expect someone to chime in about how great they are and how horrible Tesla is in comparison. Great for you, I'm not buying one of those cars in any event, so I'll never "get it". My next 2 cars are Model 3s, and my S is not retiring any time soon.
I've now just returned to midwest after several months driving mostly Tesla (occasionally eGolf). Every time I drive the other cars, I keep looking for the screen. The maps feature (and nav based upon maps and internet search) has become ingrained, and is very very difficult to live without. Not to mention having controls and other info pretty intuitively and directly accessible on UI. Do I wish Tesla nav had waypoints? Sure. Do I wish media player USB function were better? Sure. Would I trade Tesla UI for the crap nav and controls on most other cars (destination entry only when stopped, horrible maps and rendering compared to satellite view maps on Tesla, dials, knobs and levers all over)? Never.
I suspect that the Model 3 UI will be simplified over the Model S/X UI. It will be more predictive (with context-based display that is intended to match what you are doing or how you are driving). In other words, one display for parking, a different one for manual driving, and yet a different one for AP. In that process, I expect Tesla will get a few things wrong and they will be frustrating. But nowhere near as frustrating as iDrive in my 5 series, controls that reset EVERYTHING each time the car starts in my eGolf, auto engine cutoff on X1 that steals driver display every time you stop to display useless information.
In other words, though not flawless, the S/X UI is - to me - tons better on the whole than any other car. The few offenses are less annoying and intrusive than the "misses" in other cars. And I expect 3 UI to advance upon that. I expect it will include some sort of instrument display for speed etc. somewhere around or on steering wheel. However, if it does not, I'm going to keep an open mind and "live with" it a while before passing judgement. I'm expecting that, after 1,000 miles, I may very well see the cockpit controls in most cars as superfluous.
I'm also someone who likes the clean and minimalist interior design of the S. I look at all of the cockpits being posted here as exemplary, and I see them as crowded, full of plastic, and not luxurious at all. The S feels huge every time I get in, and part of that is because there is less crap in there. Admittedly, it is not womb-like, and I know that is something some people want.
I expect the 3 interior to continue that trend. And, the driver area is going to feel quite different (GOOD, to my sensibilities) without all of the instrumentation and stuff in front of the driver. If they deliver on the performance they are benchmarking (vs. BMW 3, Alfa, etc) and (hopefully) decent seats, I'm going to love having a small, sporty sedan that feels airy and roomy... with my spaceship controls.
Meanwhile, every time I drive one of the other cars... gee, I miss my (S)paceship!