Extrapolate Amazon's retail business out to the size of Walmart, $500 billion. Assume extreme retail margins: 5% net income margins. $25 billion in profit, at max size, under the best case scenario Amazon will ever see. More likely, Amazon will never reach the retail size of Walmart today (inflation adjusted).

A more likely number: maybe $12 to $15 billion in retail profit. Slap an optimistic valuation for the retail sector onto that: $240 to $300 billion valuation. Comparable to Walmart.

Next, AWS at $60 to $80 billion in eventual sales, with 20%-25% margins, spitting off perhaps $15b-$20b in operating income. That business might end up worth $300b to $500b.

All of Amazon's best case scenario growth for the next ten years, is already priced into the stock. That's what you would typically expect with a ~250 PE though.