For listening to StarCom21 anywhere in northern Illinois you need an SDS100 (portable) or SDS200 (Desktop/vehicle mounted) due to the simulcast used in the area, no other scanner will handle that properly.
For the upcoming RED Center system any P25 scanner will work, such as the WS1040. I would however suggest the BCD325P2 instead, I find it easier to use and program and it is exactly the same size and design as your BC125AT. It is more expensive but more future-proof, you can use it for Phase 2 right out of the box and (for a fee) add DMR and NXDN down the road if needed. It does not handle simulcast well in many areas, so that is why the SDS100 might be the best choice if you can come up with the money for it. That would allow you to hear all the unencrypted StarCom21 traffic such as the ISP and other agencies that use it.