From what I know, a mesh would make sense if your network spanned many kilometers. If your planned sensor network is small enough such that any node is within 1km or so of the gateway, then there is no need to mesh. As others have said, if you don't need to cover a massive footprint but do need to service 1000+ sensors, you can just add a second byte to subselect. So say you have 2,000 sensors on your network. 8 of them have a nodeID of 255 then. So the gateway broadcasts to nodeID 255 and 8 nodes awake and process the packet. The first byte of the payload could be 1, 2, ... 8. This lets the gateway talk to just one node and the other 7 can go back to sleep. In this scheme each node will wake 8 times as often as if there only 255 nodes but it is simple enough to implement with the existing library.