How is hoarding to be prevented?
Key points in bold.

Hoarding doesn't need to be prevented. At least, not yet. See this answer for a solid argument: How does hoarding hurt Bitcoin?

Bitcoin attracts hoarding by design. To change that would turn it into something else.

As Bitcoin matures, I expect that it will remain a problem that speculative trading brings  instability to the market, similar to the gold market. If you put your retirement savings into gold, you'll likely do quite nicely, but there's also a significant chance you'll lose most of it in a price crash. It's not a reliable store of value. Even if you have several years you can wait for the value to come back up, you may still lose out.

Even though bitcoins are more efficient to trade than gold and cheaper to store, it's subject to the same volatility when traders manipulate it. The more popularity Bitcoin has, the bigger the traders will be that take an interest in it, like they do in gold. This could mean that when Bitcoin is mature we still see the same level of volatility that we see today with Bitcoin (and gold).

To me, this says that Bitcoin is great for efficient online transactions, but in the long run (once the market has reached its saturation point) won't a completely reliable store of value. For that, a diversified portfolio of productive investments is better.

If that becomes common knowledge, then people will eventually accept the volatility as a necessary risk in the use of Bitcoin. After all, on average it will still almost certainly cost less than credit card transactions and traditional international money transfers. Secondly, risk-reduction services (ie insurance) tend to fill gaps in the market like that for those who don't want to take the risk.

In the meantime, Bitcoin is doing a great job, but it doesn't mean something better won't come along.