Two condensing units on a single ring main?

I have a scenario where an existing system requires it's single multi-scroll pack is to be replaced. I'd like to offer a future-proofing strategy by having two, twin-scroll, condensing units that are initially teed together on the existing ring main.
In future, when they consider replacing the evaporators, they could then install two ring mains, with a condensing unit on each, and give them some diversity/redundancy.
With two condensing units on the same ring main, would I need to install balancing lines between the units at all? If so, where?
My initial thoughts were that I would need to balance the pressures in the two receivers - in the top to balance the gas pressure and in the bottom to balance the liquid levels.
Would appreciate anyone's thoughts on this.
I have seen this scenario only once before and have vague recollections of a balancing line connecting the two in some way - just can't remember the details.

Kwaker,
Is this what you mean?

http://files.danfoss.com/technicalin...l-June2015.pdf

Kwaker
Its not advisable to connect 2 condensing units onto a common evaporator pipework system as the system charge will go to the dominant condenser and receiver as it’s almost impossible to balance the system. You will need to common the suction to the compressors to balance any oil return, also common the condenser pipe work and receivers to prevent the gas short circuiting between the condensing units. . You will basically have to run it as a rack system otherwise you will have oil control issues ,gas charge issues, plus control issues.

You could pipe it in & just isolate it for the day the other fails.
Install burnout drier in suction to cover burn out scenario.
If evaporator fails, all bets are off.