I am not sure of your location globally, but yes this is something we are doing in April for the North American market along with a kit for the hydroponic and reptile market.
In regards to expansion boxes, you can already network units together, this is explained in the manual.
For your situation i would advise on the EX upgrade kit, although this comes with a conductivity port i would have to check if an EX upgrade is possible for fresh water, I see no reasons why not. I will check for you though. If this can be achieved you will then be left with 3 free ports for all your add ons.
Basically all you are asking is available now we just need to ascertain if the EX upgrade can come with 2ms conductivity.
Moving your conductivity card on to another user really would not be an issue, there is zero ProfiLux gear on the pre owned market and I am sure it would get swiped very quickly.