Updated 2019-09-20 !
This Blogpost was initially made before the IKEA outlets was enabled in the Apple Home app. They could then just be reached via a Tradfri Homebridge plugin.
Since a while blinds are supported by this plugin but not by the IKEA Gateway and app so maybe its time again to install it ?
Another post covers the installation of the Trådfri gateway with a HomeKit approach. (Without Homebridge)
Other HomeKit posts on this Blogg