Will there be an equivalent upgrade to that of the Model S & X, that will include the HEPA-Filter upgrade for the cabin?
Ask Tesla, but don't expect an answer because they haven't even finalized the car's design. Also, no one here has anymore specs about the car than you do.
Best response ever.
I highly doubt it.
One of the goals of Model 3 is to make it simple, therefore, cheaper and faster to build for $35K. This means limiting the numbers of options as much as possible. It's not just about paying for the options by interested customers. There are "foundation" costs associating to supporting options.
For example, let say a crew neck short sleeve T-shirt has options to attach sleeves to make it into long-sleeve and neck wrap to turn it into a turtle-neck. Yes, you don't have to pay for the options but the you have to manufacture in attachment mechanism (zipper, buttons, etc) to connect the sleeves and neck wrap. That increase the costs and complexity of manufacturing.
Having color and seating material options make sense as they don't add to manufacturing complexity, as an example. HEPA-Filter is only effective on if you can property seal the interior. Unless it's just a simple filter choice vs. more advanced circulation system.
@jordanrichard pencils were down two weeks ago, musk confirmed during yesterday's conference call.