I'd love to have the option to replay Fey Meander stages after I've completed them all.
It'd be a really handy way to test out new comps and heroes against a variety of interesting opponent teams.
No need for more rewards for recompletions, but for example I'd love to have the chance to run through it again with a Frost team built around Aethereal when she drops in a week or two, or to attempt it with non-Legendary teams etc.
I think this would also make for a good source of content for a lot of streamers, being a way to showcase new heroes or strategies in ways that involve a lot of variety