Towards 1.13

[xoft]

I Assume the key is the name of the block, but what would be the value?

Nope. The map would be something like "IsSnowable" -> "1", "IsPistonBreakable" -> "0", "PipeVolume" -> "100" (there's a fluid-oriented mod out there, isn't there?). A separate map for each BlockType.

The evaluation should go something like:
1. If there's a callback, use it
2. No callback? Look for the hint
3. No hint either? Take a guess