From 2010 to 2014 bitcoin was growing by entering new niche markets: drug trade (Silk Road), gambling (Satoshi Dice), trading (MtGox), trading in China (Chinese exchanges).
It have stopped 2 years ago. Next niche markets (internet-trade, remittances, Wall-street) haven't materialized.
That means that benefits of bitcoin over fiat, for user, are not big even in niche markets to justify switching to it from fiat.
Therefore, bitcoin have to be modified, to make better fit for new markets.
How to modify bitcoin in several (sometimes incompatible) directions?
The way to do it is through sidechains.
I've made a thread about it in general section, but was advised that this topic should really belong to Economics section.
So I'm posting the link here.
https://bitcointalk.org/index.php?topic=1272599.0