It will depend on multiple things. I think Apple has opened the door for devices without the HomeKit chip now so theoretically ST could become HomeKit compatible but I’m sure they never will unless they become the last hub that doesn’t.
ST would have to program the hooks for Siri Shortcut into the app, which I’m sure would only go into the new app if anywhere, but based on how iOS is ignored since the Samsung purchase I would say that probably won’t happen either.
I purchased Workflow for iOS and have been anxiously awaiting for Apple to do something with it. I was blown away when I saw the Siri shortcuts at how similar they looked to the Workflow app.
Ultimately I use HomeBridge for Siri integration as well as the convince of having that little control center menu that lets me manipulate favorite devices and scenes from the lock screen. it’s a huge boost to wife acceptance factor. I do find the Apple Home app a bit clumsy, although I think the ST app is too. I keep finding that truly the best way for me to interface with my home is via voice, and Siri is so much more forgiving with me messing up device and scene names than Alexa.
I want it all in Apple Home and I want Apple Home to be some magical perfect app. I never get what I want though, so I make do.