More Gamma Quadrant aliens. Think of VOY and all they aliens beyond the Borg in that quadrant. I'd like to meet all sorts of vastly different beings out there. Maybe we also visit Bajor's ultimately doomed colony on the other side of the wormhole and see the farthest edges of the frontier on the other side. Deeper in, we see some powers resisting the Dominion who have yet to be conquered. Maybe also on the outskirts of Dominion territory we meet some of its client states not a part of it yet that might be susceptible to in-fighting and Alpha Quadrant manipulation. The show is more about life out there beyond the wormhole than the Klingons and Romulans here. At some point late in the series, yeah, maybe introduce the Borg. Sisko suddenly is himself a liability in developing events between the two mega-powers.
The Bajorans are going through massive social upheaval post-withdrawal and the Prophets being aliens. There are Holy Wars and ultimately a great Reformation before ultimately Bajor triumphantly, despite Cardassian manipulation and indeed a second invasion attempt, joins the Federation.
Dukat remains similar to how he was in earlier seasons where you can somewhat sympathize with him, his perspective, be charmed by his manner and dynamism...and therein lies the danger. Especially as we meet his rivals in the Central Command, Detapa Council, etc that he Frank Underwood-like outsmarts to remain our main baddie. But, you see him being a bastard and can't but hate him for the grief he gives us. You know, I hate the killing of Jadzia. But if it weren't Red Eyed Dukat (a caricature of a baddie) but a very sober bastard coldly, even flippantly, doing something awful, that might have worked better. You the viewer would want his head, and, by series' end, finally, you'd get it.