Ok, here are my ideas.
1. Change the classic mode experts to level 60, with the same loot and rewards as storm legion experts. Keep it on a separate queue so experienced player don't have to queue for them, but they would be relevant again for everyone else.
2. Hard mode dungeons for level 60. There could be 2 versions... Classic, with the old master modes and raids, unchanged, except for making them have appropriate loot and difficulty as a storm legion tier 1, 5 man dungeon.
Also, storm legion hard mode dungeons. Same thing, but new tier 1 level dungeons, with new content.
3. Take the classic chronicle duos, and scale them (like make one 50, one 55, one 57).
4. More queues in the dungeon finder! Anything not in there will automatically be less popular. That is why more people didn't run the old masters mode ones.
Include duos, hard mode duos, normal dungeons, classic experts (now scaled to 60), storm legion experts, classic hard mode, and storm legion hard mode queues.
5. Raid finder. I know people don't want something like the dungeon finder, but it could be made differently. A time and place could be made for the raid, by the organizer. Then people could see what is out there, and put in signup requests. Organizers could see everyone stats, who is online, and send invites.