Some early thoughts I had...
Most of the Commanders seem to have minor but flavorful effects, akin to how Theme Lists work for Warmachine. But not Rules-bombs like GW Commander rules. Solid overall if in need of refinement.
Each Commander does offer a distinct advantage in System Wars scenarios, usually one way or another to max out more Planetfall Points. But of course, those have to be delivered, and each P-Fall point means less firepower for shooting down enemy threats.
Relthoza don't have significantly more PF points in the core Assault fleet. (In fact, Sorylians do!)
But Relthoza can almost all approach under complete Cloak. They won't be spitting any firepower, but they're more guaranteed than anyone to deliver the troops on target. Consequently, they have VERY limited conversion value to non-System Wars
scenarios. Assault Carrier makes for an interesting Carrier option in a regular scenario, likely all about the boarding. But the Assault Cruiser and Frigates are worthless in conversion.
In contrast, Directorate, Dindrenzi, and Sorylian all are solid in conversion to conventional usages. Less firepower, but lots of Boarding Action!
Aquans convert in a weird way, offering only a cheap carrier and dedicated minelayers.
Terran Carrier can make a solid changeover with Cruisers added.
Terrans and Dindrenzi both offer new Escort options to their respective Alliance/League, crazy tough in both cases.
Looking at scenario balance, and the way scenarios limit Planetfall assets, I don't think we'll see any need to buy a second box set of these ships. But they'll absolutely add flavor in scenario and campaign, and fill gaps otherwise.