1) When will Google/Android TVs be able to be added to speaker groups?
I have gone through troubleshooting provided on several forums including this one.
2) I have also enabled the setting to allow casting to wake the TV up. This doesn't work at all.
Devices that have "Chromecast Built-in" are a bit different. The maker of that device controls a lot of the options. At first, they didn't support Speaker Groups but that should have been added as an update years ago. Check with your device manufacturer to see if they support that, decided to not support it, or are still planning on adding it.
It looks like you have things setup correctly. Does the TV show up as a casting option normally in the Google Home app?