My request would allow to create a domain specific group, for example a light group, which will actually be a light entity and not a group entity. This wil also allow to set brightness and color temperature for the group members (for those group members which support this).
It would be very nice to get this, so we could control devices in domain specific group using voice assistant.
Old-style groups can not have unique_id and thus can not have alias. That makes it unable to be controlled by the voice assistant with different languages.
Yup, that’s correct. Domain specific groups work with Assist. However mambership management of domain specific group must be manual. That is, whenever a new light is added to Home Assistant, then it needs to be manually added to the domain specific group.
Legacy groups have group.set service call, which can be used to automatically update group membership. But such group can not be used in Assist.