The datatypes category is for the discussion of the specific properties of datatypes themselves. Sample topics might include:
The evolution of BLANK! and VOID!, and their relationship to the NULL state (which is notably not a datatype!)
Representation of datatypes in the system (and whether there should be a DATATYPE! datatype at all, or if they are merely represented with more general object structures)
How new datatypes might be added...either with C code as an extension, or with user code adding behaviors to an object-like "class"