As much as I wish this were true it just isn't the case. Let's not embellish. That doesn't do anyone any good.
OP: Can a model RR be built in S? Of course! It depends on what you want though. Based off of your criteria of the 30's Santa Fe and being a locomotive guy, I'm gonna stop you right there... S is the perfect size, but you are not going to find much Santa Fe specific equipment, let alone steam in S. I am not aware of any S scale brass steam ever being done. Brasstrains does not list a single SF specific model. If you are ok with Hi-rail then you could get the Lionel AF Y-3 2-8-8-2 in SF paint as well as the American models 4-8-4 Northern (also available in scale wheels). Other than that I can't think of any more.
Not trying to be a downer, but this is where many of us live... Love the size and wish it were more popular, but it isn't. And it isn't growing. MTH buying S-Helper Service and now going out of business is a big hit. Lionel will likely keep dribbling out new products here and there, but realize that the scale Berkshires that just came out were being discussed 6-8 years ago. That's how long product cycles take in S.
I think you should decide if you want S for it's size and change your prototype, or model SF steam in a different scale.
Just my 2 cents...
I'm from Topeka and my father, grandfather, and great-grandfather were all ATSF engineers. Prototype isn't an option.
Despite the ATSF having the most trackage in the US, it tends to be No. 5 on the steam popularity list behind Southern Pacific, Pennsylvania, Union Pacific, and New York Central. ATSF was the most progressive railroad in a sense - it shifted to oil burning earlier - and to diesel earlier - so it's popularity is more tied to the Warbonnet diesels like the E8, F3, and F7 - I'd venture to guess more ATSF F3s have been sold across scales than any other locomotive.
Other than O - which ATSF gets pretty fair steam treatment from via MTH / Sunset - there's not much out there in other scales either. There's zero 1:32 / 1:29 accurate steam options - it's all SP / UP for the most part. HO is just seeing some plastic ATSF specific steamers from BLI - Northern and Mikado - though reviews of them are mixed - electronics issues. Most HO options are 40 year old brass or USRA generic models (of which the ATSF had none).
Based on what I've seen - there's basically 4 accurate steam models:
American Models Northern - ATSF was the base. 2 road numbers (but one can always add more).
S-Helper Consolidation - Baldwin base model - acceptable for ATSF
River Raisin B&M Berkshire - ATSF bought 7 in 1943.
Lionel Y-3: ATSF bought in 1945 and sold in 1947