I'm looking to do something like this:

# this would reference a TransformObject
myNode = graph.findNode('%tag(fk)')

xformValue : Matrix4 = convert( myNode.xform_out )

Basically, looking to merge the worlds of manipulating objects directly and indirectly through the apexscript "meta" apis ( generic nodes and ports vs. type specific values ( TransformObject and Matrix4 values ).

I'm not sure what's the question? The TransformObject's xform output is already a Matrix4 so I don't think you need the convert() in the first place. So I'd expect that you can omit that. But otherwise, everything looks valid?