To reclaim his position as the "Preeminent Evil Overlord of the Superverse Franchise"?
And also, to let Darkseid go from said position?
I say yes.
Don't get me wrong: I love me some good ol' Kal vs Uxas enmity, and the two should still fight, but only on rare and memorable occasions, IMHO.
But the New Gods isn't really part of the Superverse, and it's shoehorning into Superman's world hasn't done it much favor in the long run. They're trying to be their own full-fledged franchise (see MISTER MIRACLE ongoing and the upcoming NEW GODS movie).
And after watching Thanos beat the Avengers + Guardians of the Galaxy + Doctor Strange in AVENGERS INFINITY WAR, I want Darkseid to be a universal DC villain that no one alpha hero or even one team can ever handle by themselves.
There's a lot to like about Mongul. He's a far better fighter than Darkseid, and pouncing around on all fours in battle would not be demeaning to him.
You just have to make Mongul as different from Darkseid as possible while keeping him squarely in the Evil Overlord trope.
On that note, here's a wacky start: give Mongul hair on his head. Seriously, look at Superman's rogues gallery and count the number of bald/hairless males versus non-bald/hairy males and you'll see the discrepancy.
Oh, and Rogol Zaar (or whatever his name is) sucks big-time and is not eligible to take Darkseid's place.
EDIT: Of course I misspell "it" as the 2nd word in the title of the thread! Mods, can you please fix it?