What good is having $35,000.00 car that you can’t product. Let assume that the mark-up on all Tesla’s S, X, or 3 is the same. You are charged with setting production rates. The mark-up on each car being 30% and you have limited production. Your going to build 100,000 3’s at the cost how many “S” and “X” cars. How long do you think you would remain in business?
You are assuming that the Model 3 will use the same production line as the S and X, which is highly unlikely. It will be built on a different chassis, and likely have it's own line(s). So producing Model 3s won't reduce the number of Model S/Model X cars that Tesla can make. You are also assuming that people will buy the $35k base. Which is unlikely, they will probably add lots of nice high margin options. (Not to mention that Tesla tends to produce all of the highly optioned cars first, so they won't start making the stripped base versions right away.)
Tesla has made it clear that they have lots of room for production. For example their paint shop can handle 10,000 cars a week. (And they are talking about getting up to 1,000 Model Xs per week in the next quarter.)