Have you ever had any experience with Laetacara curviceps? Seems like an interesting tank mate for the Keyholes.I wouldn't go as far as to guarantee it, you can't always predict how crazy a fish gets with breeding hormones, but from my experience I'd try it, could make an interesting tank. For me, rams have been feisty enough to stake out a defensible nook in a reasonably peaceful SA community, including some larger fish, like Mesonauta, or a big angelfish pair. They were bigger tanks, but also larger and more fish.
Of course, with a keyhole pair, you could end up with some fry to deal with. I've had breeding pairs, such as geos, in community tanks, which meant I could choose to save fry and siphon them out to raise in a growout tank at some point, or let nature take its course, in which case a few might hide well enough to make it anyway, which may or may not happen with a BN and plenty of tetras in the tank.