The Model 3 interior is the first step towards an interior optimized for FSD - removing the separate dashboard display and rotating the display to landscape that is better for displaying videos.
The next step will be figuring out a way to reduce the presence of the steering wheel, along with other changes to the interior focusing more on keeping the passengers entertained while the vehicle drives itself - such as some workspace, 110 outlets, rotating seats, ...
As to when we'll start seeing these interior changes in the S/X - we're all just guessing. Though if Musk is right and the FSD software will be "feature complete" late this year, we could see S/X interior changes in the next 12-24 months - and earlier if it would allow Tesla to simplify and/or reduce the cost of manufacturing.
FSD won't be good enough and legal for use unattended for at least 5+ years, in the meantime they should continue to make cars that are not annoying to use when operated manufally.