as Satoshi said, you will either be a millionaire or have nothing by 2020
(you can easily find the quote)
I think you mangled the quote. Here's what I believe you're referencing:
... In a few decades when the reward gets too small, the transaction fee will become the main compensation for nodes. I'm sure that in 20 years there will either be very large transaction volume or no volume.
First off, he's talking about 2030, not 2020. Second, he's talking about transaction volume, not exchange-rate. Obviously, though, if transaction volume is "very large" in 2030, it means bitcoin did indeed achieve market success; thus, it's reasonable to assume it commands a good deal of purchasing power.
And third, let's also note that he was saying that it'll be
a few decades before transactions fees become the main compensation for "nodes" (mining-nodes). This design/intent is directly contrary to what people who want to keep the blocksize at 1MB at currently saying.