The polycrystal builder in 2019.03 (and probably some earlier versions, but maybe not very old ones) works fine with hexagonal and tetragonal original crystals. It doesn't generate a hexagonal supercell, but I don't see any need for that (note that any hexagonal cell can be converted to an orthorhombic supercell).
Ulrik's point 3 should be disregarded as this plugin is not released with source code, as most other plugins are.