Ribbon Cable Noise Susceptibility
If the ribbon itself is mostly shielded by steel plate from the major sources of industrial plant noise, this will help.

If you have enough spare wires in the ribbon, you should separate each differential pair on each side with ground wire signals, and keep one side dedicated to the serial signals, while the other side is all of your analog pairs (again, make sure to separate unrelated pairs with spare ground wires).

You can actually get a shielded ribbon cable with twisted pairs already organized for you, which would be great for differential pair serial comms and for the analog signal pairs. You can get some at Digikey for example: here  and datasheet here which are "3M" brand and you can get 30 metres for $1050. I'm sure buying direct in larger amounts would make a huge saving, as Digikey only offers these as "value add" which can be grossly priced. Not including tax, this makes it only $1 of cable for your 300mm you want per unit, for the full service of shielded twisted pairs in an easy to assemble ribbon cable, which can be easily IDC terminated and grounded on your PCB/chassis ground.

The capacitance is just as bad as similar multi-core cables I've seen, between 15-30pf/foot, and I've run gigabit ethernet over similar capacitance in twisted pairs in custom cables over 5 metres so i'm sure this will do whatever communications you want in addition to your analog signals. 

With your signals being +-10V and such a low frequency filter on the other end, i'm sure un-shielded will still be fine, provided you try doing the signal types as far away from each other as you can, using blank ground wires between each different pair.