I think this is a very common meme about what success means for bitcoin and it's tied up with a misunderstanding of what money is; most people think money is valuable because it's used transactionally. Rather, money is valuable because it has reservation demand. An increasing level of transactional usage might increase reservation demand but it doesn't need to. On the other hand increasing reservation demand can occur even without any new transactional demand. Moldbug explained this best in his discussions on bitcoin and how money is a bubble phenomenon:
http://unqualified-reservations.blogspot.com/2013/04/bitcoin...
http://unqualified-reservations.blogspot.com/2011/04/on-mone...
Bitcoin can be "successful" even if it's not the preferred medium of exchange for most, or even many transactions. It can act as a store of value just as gold does. Except it is superior to gold is almost every way - more fungible, more verifiable, more divisible, easier to transport (especially across borders) and easier to transmit. A success case for bitcoin is that it becomes Gold 2.0. Gold's market cap is approximately 7 trillion. Bitcoin's market cap is approximately 6 billion. If Bitcoin were to replace gold as an alternatively medium of savings (say, in 50 years), its price could be hundreds or thousands of times higher than it is now without needed much, if any, increase in transactional use. Gold has almost no transactional use but it has a great deal of reservation demand.