1.) What would happen if a dapp runs out of RAM?
When RAM is insufficient for a dApp, some operations are unable to carry out and smart contracts cannot be deployed.
2.) What was the change between Dawn 3.0 and Dawn 4.0 in terms of the RAM market?
Under the Dawn 3.0 system contract, token holders can only sell RAM for the price they paid, just as the other resources. You can check more details in Daniel Larimer’s article. EOS switched to a market-based allocation approach using the Bancor algorithm from Dawn 4.0.
3.) What are the benefits or having a market based model for RAM staking?
With the market-driven model, a dApp dev can receive capital gain from un-staking his RAM, and therefore willing to free the resources.
4.) What are the drawbacks of having a market based model for RAM staking?
As more dApp developers join, and more data needed to be stored for a long time, more RAM used is extracted out of the market, making RAM more and more expensive.