Design is far more than just what is seen as a guest. It includes how everything, literally everything, goes together.
Hypothetically, let’s just look at the bathrooms as an example. This won’t be specifically about the bathrooms in the TRON building but I know it does have Cast Member bathrooms and that Chinese and US regulations do not align. Bathrooms are an area with very specific regulations, especially when it comes to accessibility. The following are some of the specific regulations that a wheelchair accessible toilet must meet: height, distance from the wall, clear space around the toilet, location of grab bars and location of the toilet in relation to the stall door.
Let’s say the accessible toilet, which is in a corner, has to move to the other wall. That wall may not be big enough to hold the plumbing for the toilet, so it has to get bigger. If it is a wall mounted toilet then the wall may be getting even bigger still. How does “stuff” get out of the toilet? You have to move those pipes too and they have to maintain a certain slope which means they could be taking up more space. And what is on the other side of that wall that had to get bigger? What if there is other equipment that has certain to be in a certain sized room that just got smaller?
That’s just a few issues that could arise in moving a toilet. The structure needs to be redesigned, or maybe even changed completely, for the local soil and wind loads. The HVAC system needs to be redesigned for the local climate. The electrical systems need to be redesigned for the local power supply. The location of waterproofing on the exterior walls might change based on climate. The type or amount of insulation can change based on the climate and energy codes. Emergency exit doors have to studied to ensure they are in the right locations, maybe more are needed or the exit path needs to change. All of those changes can and do have ripple effects like the toilet example above.
That’s just the legal and due diligence changes. Then there are possible operational or creative changes, even if minor. Ratatouille has an upcoming closure to fix its floor, so it makes sense to not make that mistake twice.
Steel coasters do routinely go from idea to opening day in 18-24 months but they are also not a lot. Most stations are little more than a roof and the maintenance area is a rather simple shed. The coasters themselves are all fabricated offsite and then assembled on site.
When did fabrication of the rooms start?
You are way off.
Look at slide 6 of this presentation:
https://network.aia.org/HigherLogic...tFileKey=25eadd48-6fff-4a2f-ae26-cef8a77d4f6d
Disney very often announces projects shortly after the Feasibility phase. There are exceptions like the Skyliner but it’s quite common, even with TRON. The
end of Schematic Design is usually considered to be around 20% completion of design. That’s a lot of design work left to be done
after an announcement and even at least some sort of art release. “Working plans” are not done. This is also why a project site will sit untouched after an announcement.
Approvals and plans are not done before the first dirt is moved. For large projects Disney often makes some use of the fast-track process where design and construction are overlapped. You don’t need a finished design to start site work, you don’t even need a finalized building footprint. Look at some of the South Florida Water Management District permits and you will see some that are just based around a general area and not any specific buildings. Even parts of actual vertical construction can and are overlapped with design.