The analogies actually make very useful and subtle distinctions for my/our own experience. I'm getting ready for work and will just add a quick comment but I have a feeling there will be others before I return.
Where I start to fall down in my understanding is in the difference between co-presence and co-hosting. Are these not the one and same thing?
There is a difference in general parlance. We in my system are now looking at co-hosting as applying to a broader period of time, but that's not the only definition. If there are two alters who are effectively out most of the time and running the show, calling most of the shots, directing the life, that's what we're looking at for co-hosting. They wouldn't necessarily, and in our system wouldn't be out at the same time, though they would be entirely co-conscious.
Co-presence in the both-there-but-unaware-of-each-other would explain how sometimes a little will come into the body at the same time as someone else and there is a minor skirmish, for example, over what the hand is doing. So the hand reaches out for something, as if one alter is saying "I want to grab that" and the other is saying "wait, what's my hand doing, come back," and the hand-arm gets stuck sort of in mid-air in a mild tug of war.
Now John and Jonathan both feel they wrote much of the above. So we're not sure what the heck that is? Co-operative co-presence? No, we don't want to go adding a new bogus definition to the pack. Okay, John, that was you, I rarely use the word bogus. The distinctions are quite useful in pinning down what's happening. We have a subjective experience but aren't entirely clear why it's happening that way. Terminology leads to normalizing this confusing "disorder."