Note that for a stiff low-impedance DC link, it may be harder to inject and detect than on an AC power line.
Devices running on AC power line naturally need rectification and EMC filtering components, which also provide a separation for communication injection and detection.
With a well bypassed, low-impedance DC bus, you don't necessarily have that. I'm not 100% sure you can do it very easily, without adding cost to every device, think about extra DC bus filter components.
A one-wire or two-wire communication, even bog standard CAN bus, might be lower in cost, including extra wire installation work, especially if you work for the total development cost, unless you are going to produce thousands of installations with hundreds of meters of DC bus per installation. But if you were to do that, why wouldn't you simplify the problem for that specific case, reducing modularity?
As a general note, such modular systems are not going to be cost-optimized anyway, so I wouldn't try to save on communication wiring.
Instead, for ultimate cost reduction, look for maximizing integration, so that you minimize the amount of DC bus wiring altogether - and solve the communication problem at the same time. In essence, this means, whatever "power optimizer" means, it could be a feature on your inverter or battery charger instead of a separate product - done on a single MCU, no communication needed.