Remote I/O with two PLCs

Hello,

I have a controls contractor who is proposing that I use an existing remote I/O rack (Control logix AB)that is largely empty, in conjunction with a new PLC that they are installing. They would be installing some new modules in the rack. Therefore, I would have an existing PLC (that the remote I/0 was originally installed for)communicating with the rack, as well as a new PLC communicating with the rack. Is this possible (I think it is), and if so, is it wise?

I dunno about wise....
What type of communications are established between the CPU controller and the Remote I/O Rack?
In case of a ControlLogix system with EtherNet/IP or ControNet Remote I/O, any Input type module located within a Remote Rack networked within the multiple controllers' topology could be "owned" by all Logix CPUs (connections established within each CPU); however, any Output type module could be "owned" by only one processor; the other networked CPUs could only "listen" to the Output module "owned" by another controller.
Yes, I have seen it done and it could be viable, however, I really don't see any practical advantages but plenty of headaches down the road...
If the Remote I/O rack data is needed within another Logix system, Produce/Consume will be my approach.

that depends

do they propose using produced/consumed tags or messaging
the I/O back and forth.
This is also up to you. If it was me and I had no use for the
IO data from the modules they want to install into the old chassis, for the process running in the existing PLC, I would tell them to install a new chassis, however
if the data has some benefit to the process running in the
existing PLC then I would do a Produced/Consumed setup
just for that IO for the new PLC.

If you want to be conservative, install another network bridge module just to serve the new I/O modules.

ControlLogix 1756 was bult to do exactly this sort of thing, so I say take advantage of it.