I experimented with the modular armor today. It looks like it’s mostly not implemented, even to the degree laid out in the GTExtras thread.
Oh, plates work, but nothing else does. Motors don’t reduce weight, batteries (at least Large Lithium batteries) aren’t recognized, and only the IC2 circuits work. You can’t, for example, insert a Processing Assembly into a Modular Exoskeleton at all. I didn’t really look too closely at how a full suit of the stuff at max weight w/o motors compares to, say, regular steel armor.