I really like battleleves for their varied (kinda) content and worldbuilding lore they contain in the text.
I'm grinding levequests now and would actually be pleasantly surprised if they came back for EW areas. Though I don't actually hold an expectation for this.
I also very much enjoy the leveplate stained glass artwork, always have since we first saw them before 1.0 came out.
There was once a business card holder in the style of one and I wish I bought it when I could have.


As for repurposing them, a simple idea is to keep them fundamentally the same, but scale up the difficulty a ton. Make them challenging. Make levelinking a thing people will want to do so players can help each other.
Putting a reward you can get 6/day of such as a materia cluster or something on them would perhaps get people doing them. And the nice thing about levequests is that they're in the overworld, so you'd see slightly more activity when you're out doing whatever unrelated thing you happen to be doing. I think just the general concept of seeing players out in the field doing stuff is a great thing to strive towards. Everyone afking at home or in town is kinda lame, not going to lie.