I don't actually think it was an Ancient Device.
Subspace beacons are entirely doable with current technology.
I liked it a lot. I loved seeing all the system-lords again. Brings back all the memories of 8 years of SG1.
I feel like they should have mentioned the Asgards or whatever, but I guess that they've been destroyed by the Replicators and never became human form. Maybe they're all chilling with the Asurans (next highest level of technology? )