FlatSix911
Porsche 918 Hybrid
Free is just a 100% discount. Once free is expected you'll have a hard time getting customers to accept paying for it. There are a thousand internet companies that can attest to this. They built up a customer base on a free service to find that those customers weren't willing to pay for it later.
You can read these very forums to find model 3 reservation holders that were upset to hear they had to pay to supercharge.
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