This thread will be used for status updates on the update to 1.13, so feel free to subscribe to updates to it.
I had a quick look tonight with a view to testing out 1.13 on my test server, but SpigotMC.org recommends against upgrading to it for existing worlds, warning "There are still known issues in Vanilla which can cause item loss in chest blocks."
So, it sounds like it's not a good time to consider upgrading yet, and we should wait until things are likely to be smoother, rather than people losing items as part of the upgrade - I can't see that being popular

The item loss seems to be down to MC-134115: https://bugs.mojang.com/browse/MC-134115 - affecting double-chests which happen to sit across a chunk boundary, causing them to lose half their contents.
So, I'll watch for that to be fixed first before we do anything about upgrading I think - don't want anyone losing loads of items.