Here's my idea for moving stuff over(if it is being done... I didn't think it was but I was told Pix is going to transfer an area of chests over).
I know burying them in bedrock sounds like a good idea at first, as I thought of it too... but it wouldn't work out that smoothly I imagine. As soon as you break the bedrock to let the player get to their stuff anyone could get to the chest.
My idea is to go out or underground and build a large room out of bedrock. Fill the entire thing with lots of double chests. Lock them all. Set up a warp there, and let people claim a chest. However, it would require an OP to remove the lock and allow them to lock it, to stop people from claiming all the chests. They'd also have to place a sign on top of the chest(probably by putting fence posts on top of the chests) with their account name.
Then, before the world is converted over to 1.9, //copy that portion of the world. Paste it into the new world. Then before the world is public, have OPs go through and lock all the chests with the account names provided on the signs. This will prevent any sort of theft.