I think expanded will remain unrotated for at least this year, I doubt they'll rotate the entire BW block just like that either.
I could see them leaving Expanded as BW on indefinitely as well because BW marked a major shift in design philosophy back to something that looked a lot more like base set than the game has at any time between the tail end of the Neo era and HGSS. There are hints, some people have argued, that they want to slow the game back down. But cards like Phantump/Trevenant GRI and Darkrai-GX are signaling to me that they aren't really focusing on that in practice.
I think that people are right to worry about 'card glut' in expanded where there becomes such an extreme variety of cards that it gets hard for newer players to get a grasp of what's going on in the format, but for me, that's a long ways off. Hopefully if they ever do start rotating expanded they start providing support for Unlimited as a format in some manner, with a common sense banlist (ie no super energy removals, hell just ban all of the trainers in base set plus a few others like chaos gym and broken time space).
I don't see them doing much with Legacy offline since it's explicitly an 'old cards only' format that doesn't work to advertise new cards/sets in any way.