I can see an arbitrage here. If you own a 6 year old cheap car and had it for 3 years, you go and buy a Tesla and get a 250k discount. Register the car, and then sell it immediately for its market price without driving a single kilometer and make a handsome profit.
Tesla marketing and legal should make a plan to match this demand (buyer) and supply (ppl who got a old car to scrape, but not interested to buy a new car). With the Tesla as middleman platform, buyer can still build to order their dream car, and sellers can take advantage of any financial benefit provided from the platform, without actually paying to buy a new car.