One thing that I love is the Brave and the Bold series. I'd love a modernized version with Bruce traveling the DC universe teaming up with various characters. I can also see the Cartoon series antagonist Equinox appearing as the main antagonist. I think he'd be a good villain for a Brave and the Bold reboot. Especially if the series had Batman teaming up with both heroes and villains. As for how Equinox could be revamped I can see his origins being every much the same with minor changes like when Death Metal ended the Lords of Chaos and Order took a piece of both Darkseid and High Father's powers (with a bit of their own) and gave it to a child but the influence of both sides was too much and he snapped.
Part of why I like this idea is Equinox would be a perfect villain not just for Batman but the League and I'd love him doing things like kidnapping both Superman and Lex planning to kill both for the sake of restoring balance. I think his purpose could even be something as simple as to prevent another Crisis. Like he could prevent a Crisis by keeping both sides from ever gaining a upper hand. Plus Equinox has a compelling motivation that I'd love to see play out in canon and I love the idea of him siding with heroes one minute then villains and sometimes switching sides all the while never really taking a side.