will duchies (or their names) be shown on some of the maps? at least the current system is anchored... you can just about imagine the duchy of grehk, for example, eventually migrate all the way off to the north west corner of bt.
Not on the current maps. Perhaps if the map is ever replaced by a new system, we can do more with various overlays.
will tax still be received in gold when inside duchy?
Probably.
will huge duchies get some sort of inefficiency penalties?
Maybe, maybe not.