I found that it looks like the Alexa team has just added native support for this type of capability last month:
Developer Feature Requests Support for blinds (or shades) in smart home with open/close/stop/move to %...Hi Alexa,1. There is not BLIND or SHADES as Display Category availabe -apis/alexa-discovery.html#display-categories, so please can you add support for this ?2. Blinds (or shades) can be opened, closed,...