The 'final crash' idea is a new one to me and I would like to think it won't happen. But:
If the big banks and central banks realise bitcoin is going to happen whether they like it or not;
If some of the world's wealthiest are beginning to put serious money into bitcoin both increasing its value and devaluing the fiat they're taking it out of;
If they are realising that it's game over for the fiat game as has been played for the best part of the last 100 years;
If they know they currently, but if they're not careful temporarily, have more buying power than anybody else;
...why they would not deliberately pump, forcing everybody out of fiat only to then diversify into pms and other assets at the top, deliberately dumping bitcoin to promote their new fiat currencies? It will be their last chance to keep as much of their advantage (in terms of relative wealth) because the days of 'magicing' money into existence will be over.
Imagine if Janet Yellen and the rest of the top brass at the Federal Reserve woke up this morning and suddenly grokked everything there is to know about bitcoin, and decided to buy up as much as they could. They would print up some small sum -- 5-10 billion or so, just pocket change for the Fed -- and buy as many bitcoins as they could. Imagine they could get a significant percentage of all bitcoins -- one million or maybe several million. Can you imagine the long term consequences? I seriously doubt that they would do something that ballsy and smart at the same time. But it would be an interesting scenario!