Yes, I can see with a proprietary system for a single manufacturer it wouldn't be difficult to implement, and I'm not surprised that it's been done, I should not have said can't. I was thinking about generic planners like GAP- it would be pretty daunting to connect to all the different computers, each of which have different algorithm implementations... Possible, no doubt, but it would be hard to keep up with. You could, of course, get decently close by just manually entering the previous dives.
We thought in to Cobalt it made sense to include the planning function (with a useable interface) in the dive computer itself, so it wouldn't be necessary to bring along a laptop for that capability. You can do general planning, create deco schedules, and plan gas requirements on the Cobalt. It has the advantage of being able to start with your current state of saturation, and the disadvantage of working within the limitations of a small screen. Desktop software is much quicker for comparing multiple scenarios- if you have it available.