It's been a while since I've been on here, so I thought I would check in.
Like everyone else, I'm patiently waiting for 1.13 to drop. I've taken the time to look at the save file formats, and I've written my own 1.13 mapper because the mappers I was using aren't getting updated fast enough.
It's interesting having a look at just how different Minecraft will be once 1.13 drops. The "flattening" is particularly interesting, a complete overhaul of the save file formats. It will make modded a lot easier now that the blocks can be saved in the save files as "minecraft:stone" or "custom:fancyblock" with equal ease. It looks like support for custom biomes is also coming. I haven't seen anything announced officially but the save files now handle biomes a little differently.
I've reported 13 bugs in the 1.13 snapshots (I was first to report nine of them) including two bugs that have been in the game since 1.8. Having my own mapper helps.
I hope everyone is well. Watch out for creepers.