I went through this myself and getting into polypterus reinvigorated my passion for the hobby.I have been keeping new world cichlids continually for 15 years now and after lots of thought and a few false starts decided it's time for a change, so as of next week I will have an empty tank.
At the moment I am back to just the one tank, 76 by 28 by 24 inch high about 215 us gal.
Still not 100% sure on stock yet.
Option 1 Channa pleurophthalma group of 3 to 5.
Option 2 Hepsetus odoe with Polypterus endlicheri or delhezi.
Option 3 hoplias spp, but at the moment malabaricus and aimara are the only ones available, aimara get way to big, mala I think would need tank mates or it could be a boring tank.
Option 4 stick to what I know and get a amphilophus spp of some sort.
Any ideas and opinions welcome .
I say option 2 minus the del. Some combination of Endlicheri, lapradei, ansorgii, congicus (my fav), teugelsi, ornate and weeksii would work well together. They aren't high octane but when they put on some size they are quite impressive.
If you ever get he itch to grab a cichlid again it will mix well with Polys especially if it's a herbivore.