It's very easy to setup a buy order ladder since everyone have fiat money, but it is more difficult to build up a sell order ladder since that will require huge amount of coins
Unless supply = demand in each and every country, international transfers will still need to happen.
The localbitcoins.com could use an automated market making system to adjust the bid and ask price for the largest 6-10 dealers' order
For example, if the demand for bitcoin is too high (Too much coins were bought from those dealers in a short time frame), they will automatically raise the bid/ask price for those large dealers, thus reduce the demand for coins. If the sell pressure is too high, they will lower the bid and ask price for those large dealers, thus increase the buying support. How much to raise or lower is the question here, it should provide low slippage but still enough flexibility
Sure, but if prices get out of whack people will start importing bitcoins from other countries and exporting their fiat to keep prices in sync. Doing this in a decentralized nature will still likely be way easier than a handful of major institutions attempting to move millions of dollars in 4-5 figure increments.