: (Kinda-related: I still wonder why Matt Soell hinted at a connection when
: there's no fitting the worlds together. Just to encourage speculation?)
Many things were disrupted by the whole Microsoft (?fiasco). Myth properties went to Take-Two, Seropian split, and that whole Phoenix project rather died out. I don't remember; I didn't follow the Bungie developments much during those years, for that and other reasons.
There are a few or more reasons to put several story worlds together in one big connected universe, or multiverse, or whatever you will call it. One of them is to make the total seem larger and more diverse. Another, especially as seen with the often ad hoc approach taken by several franchises, e.g. Marvel and DC, is to permit cross–over stories.
Whether any of those were planned with Myth and the Marathon–PiD universe — we can't say for certain. It's not like Myth's world seems to actually takes place on Earth, even if in a mythological phase.
The idea of a millenial cycle has occured in many stories. Maybe Bungie had other plans for that 1000–year trajectory of the rogue star; then, when they — minus the Greg and the Double Aught people — decided to work on Myth, they used a similar premise simply because it has mythological ramifications.
It is also possible that, as you say, Matt was toying with us.
I mean, he did once say — and I am unable to locate the quote on this — that the Marathon story was full of loose ends because it was being contributed by more than one person, i.e. Jason and Greg especially, who didn't unify their work. I really wish i could remember where i read that. Maybe it was censored.
Of course, it could be correct.