IMO it's impossible to "decentralize"/prevent manipulation the price of the bitcoin. People who have lots of money (whether it's Bitcoin, altcoin or fiat) can manipulate bitcoin price easily, even making FUD/buzz news could make Bitcoin price move significantly.
Decentralized exchange or OTC could reduce current problem since exchange won't able to make fake volume/trade and most people don't bother with it yet.
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But first we probably need a scalability solution, like LN or (or better: and) sidechains.
We already have the solutions, but it's far from ready/stable/user-friendly yet.
But current Bitcoin community only interested on LN along with channel factories and Eltoo. Other sidechain/off-chain such as nimblewimble are ignored and the developer eventually make their own cryptocurrency for the development.