It seems as if an always on OLED display would be the major source of battery drain - and so I don't get why watch makers haven't used e-ink. Come into the market as Timex and not a Rolex. A simplistic device which displayed time and push notifications at a $50 price point seems like it'd quickly dominate the market. Heck, you could even make it an e-ink background to a nice analog watch for that matter (although that'd probably up the total price). This sort of thing wouldn't need the processing power (i.e. more battery drain) as the current giant glossy types either. Perhaps I'm being naive, but I don't get the high-end luxury approach.
Open API would be natural too; especially given a low price point this type of watch could quickly be a community favorite.