Per the Ethernet connection - no, our current PLC does not support it.
Per the bunch of analog cards - no physical room for another chassis.
Per the CT with switch - no, we do want to display the current -- each zone may have multiple heaters, so if the zone had three heaters and should draw (e.g.) 30A and one burns out, we would see only 20A. I know the on/off CT would notify that, but staff is accustomed to bouncing needles on meters.
And on that note: Measuring the overall total draw will not work as each zone can cycle on/off independently.
But I thank you for the thoughts; I will check on two of your suggestions.