I don't think Harley going back to her classic costume is really "regression" (and with the Birds of Prey movie having a female director and writer, maybe Margot Robbie will wear it in the DCEU as it's more modest than her Suicide Squad outfit).
Also, I think she will become more heroic than villainous after this event. Dan Didio claimed her to be DC's "Fourth Pillar" after the Trinity, was heavily rumored to have told King to make her one of the protagonists in HiC, so I think she's good. OTOH, I suspect Didio doesn't care much for Ivy as he told fans on Twitter that she "dilutes" sales (which I assume are Harley's sales) when used in an independent capacity and probably told TK to kill off Ivy in HiC (despite King's protestations and "taking one for the team").
Just speculations re Didio but I honestly believe he was the biggest reason Ivy was repeatedly reduced to be Harley's sidekick over the last few years despite many writers using Ivy independently in strong, captivating stories.