Update: I'm sure Hubitat will get to adding this support to their own Alexa skill eventually, but in the meantime, I created my own Alexa skill that talks to the Hubitat Maker API to control window shades.
It's not a published skill. It's code you can use to host your own skill. I haven't written much instructions, because if you know how to host and install your own skill, you won't need my instructions.
Definitely proof-of-concept code, and I look forward to retiring it when Hubitat adds this support to their own skill.