I think they could possibly offer the J1772 + 1 adapter of your choice at no cost. Would be the smarter thing to do and also reduce cost
Since many (maybe most) Model 3s are built before being matched to owners, it would be impractical to put in a custom Mobile Connector bundle at the factory; that would have to be done at the local delivery center. Thus, each delivery center would need to stock a variety of Mobile Connector bundles (or perhaps Mobile Connector bundles without plug adapters, and all the plug adapters) and match them to individual orders. There would inevitably be out-of-stock situations in which customers would have to accept an adapter they didn't want in place of the one they ordered, at least temporarily. It would also complicate the ordering process, and I'm sure a lot of people would end up ordering a plug they couldn't use. In both cases, there would be returns/exchanges to handle, as well as increased labor costs at the delivery centers. I'm not an expert on this sort of thing, but my suspicion is that this more complex logistics would cost at least close to the $35 that a single adapter costs. That extra cost would have to come from somewhere -- either out of Tesla's (currently tenuous) profits or in the form of an increased price on the cars. If the latter, then there'd be little or no monetary advantage to buyers of doing it that way.
What's more, even though you may not think you want a NEMA 5-15 adapter for charging on 120v, those are far and away the most common type of outlet in the US. (At least, based on the outlets I've seen in homes and workplaces.) Thus, for emergency on-the-road charging, or even for charging a Tesla regularly in Some Random Owner's Home, although it's slow, the NEMA 5-15 adapter is the option that's most likely to work. For charging at home on a regular basis, it's obviously sub-optimal; but given the wide array of customer home charging scenarios, asking customers to pay $35 for a 240v adapter on top of the tens of thousands they pay for their cars is not unreasonable. The bulk of the cost of the Mobile Connector is in the control "box," the cable to the car, and the car-side plug. That $35 adapter cost, and the hassle of ordering it, is trivial by comparison.
