Exponential growth never lasts indefinitely. This means that growth of bitcoin economy will eventually slow down.
Of course. But with $30 trillion plus squirrelled away in offshore assets (tax havens and the like), there's a huge untapped market. Imagine even 0,1% of that piling onto the bid side of the
BTC exchange markets. The huge question is, how does that money move its way thither? It's not like it's that easy just to go and buy up $50 million worth of bitcoin in one go right now.
This also means that all debt based currencies i.e. USD, GBP, EUR etc are intended to fail eventually, by design.
History does hint at that, doesn't it?