It's very possible with two (0r more) HomePods. In our home I have two HomePods in the living room, set up to play in stereo, either from my Apple Music library OR as the speakers for the Apple TV (series 4)... I also have a HomePod in the bedroom/study.
I can ask Siri to play separate playlists in the two locations, or play whatever I want in one of them, nothing at all in the other. Or, more to your point, I can have been listening to a playlist in the living room and simply say, "Hey, Siri, play the same music in the bedroom" and she will, exactly the same, so as I walk from one area to the other, there's no break.
These are all on the same basic wi-fi network, or course, (although one is on a wifi extender).
Anyway, I've never had any difficulty at all having them play in that way.