After following Apple for a long time, I'd take a guess and say it will be a while for custom watch faces, Apple has only recently started allowing developers to create 3rd party extensions (keyboards and such) but that was after quite a few generations of iOS. They will probably add a few in-house faces with the next AW hardware release, but probably won't allow 3rd party faces until they have enough metrics on how often people switch their watch face. Mine pretty much stays on modular, but I'm with you on wanting custom watch faces.