This is currently overlapping with a couple other methods or will be with other planned changes

• BREAK and WRENCH should be rolled into IPart#getDrops(). See #5169 for further details
• PICK should be provided by something like IPart#getPickBlock similar to Block#getPickBlock()
• WORLD and NETWORK are more of an internal case and are probably obsolete with the changes in #5170.

What return type would you consider for getPickBlock? Parts usually don't have blocks.

by vanilla behaviour i would say return the itemstack of the part that is under the cursor (at least this is what i see ender io doing)

Just like currently the item. I guess we can argue about the the name and potentially call it IPart#getPickPart() or something. Vanilla also returns an itemstack and calls it pickBlock (or at least mcp. no idea how the official mapping is)