I work for a large enterprise that is full of product managers and layer upon layer of product and design teams (+200k employees). My personal take is that Elon Musk originally intended for the Model 3 to have some type of advanced HUD or "next generation" display that was indeed "spaceship like" and would knock our socks off. This was very clear in his opening round of tweets. He had clearly seen an interior experience ( UI/ UX / CX) along with an interior design aesthetic that had to have been better than today's best "S-class" Mercedes interiors (which are pretty amazing at night)...
However, after his tweets and comments, it appears to me that the product managers and various product owners pulled him back in and told him the Model S/X must always be their luxury brand and got him to buy into the typical auto product line / mentality. What I believe is that the original "spaceship" model 3 interior / HUD will be put on the Model S / X - my guess is that this would occur the same night as the Model 3 final unveil. I think they will show two tricks up their sleeve.
I believe they will show their $35k model 3 as promised.... and amazing changes to the Model S/X that were originally mentioned by Musk last year. In the end, I sense that Musk realized he can't cannibalize their $100K+ product lines.
Plus, he knows there is a significant % of Model 3 reservations holders who will just upgrade to a Model S / X if it has the new spaceship interior. Those assembly lines are up and running. So moving the spaceship like interior (and or HUD) to the Model S / X helps him in multiple ways. Its a higher margin, the S/X lines are running at higher scale, this removes some of the strain and backlog of M3 reservation holders, it further establishes his brand - particularly in other European and Asian markets... etc....
After the spaceship interior / HUD reveal, I would suspect Tesla to lock up plans for at least 2 Gigafactories outside of the USA to better handle global mfg & distribution. Having the spaceship like interior on their highest end product just makes it that much easier to attain funding. The stock will blow thru the roof, capital and debt markets will open their pocket books and the cycle keeps going.
Tesla has hired some of the best interior design talent out there. Do not underestimate what designers can do when given free rein to blow your socks off. I suspect they havd something special for the M3 but moved it over to the S / X for a plethora of reasons - including the need to avoid a repeat of the headaches of getting the Model X out the door.