No. Mainly because my iPhone can take care of specific sounds, when I want the Watch to be new more nuanced And subtle. And I primarily disable any tones on the Apple Watch, aside from the haptic feedback.
I would rather have more custom watch faces then I would customized tones.
What I wouldn't look forward to (and, for a minute, let me get all high-and-mighty) is the clang of crappy tone choices calling out from people's smartwatches. Most custom ringtones I hear already are pretty crappy, and I think they would be at odds with the intent of a smartwatch, which is to be subtle and only known by the wearer.
I've narrowed down my phone's custom tones to the insignia/comm badge tap from Star Trek:TNG for text messages and a snippet of the main musical theme from the anime Paprika. I could see these as being reasonable on a watch, but if the door opens for me, it opens for everybody, no matter how poor their taste or judgement.
As it stands now, the AW's tones evoke the sonnerie from minute repeater and alarm watches costing five figures and up. I think they're great.