Great stuff Serack, certainly all very plausible. I can certainly see how Mother Winter and other destructive Powers might have Outsider origin, but as they are not "true" Outsiders they are still "for Reality". They are also able to fulfill their various duties as cleaners, wardens etc. Winter serves a special purpose in the DFU, and Summer exists to check and balance it.
I do think that a small spanner in the works is the Prince of Darkness. He isn't against Reality per se, according to WOJ, but he is against the idea of Free Will (or something to that effect). I do wonder about his purpose (either initially or currently). Interestingly, Lucifer is means "Lightbringer" normally interpreted to mean the knowledge-bearer (and if there is a theme in the Genesis, it is that knowledge is dangerous), but he is often referred to as The Prince of Darkness (named in DF) which is almost the complete opposite - these two ideas seemingly at odds. Perhaps he went beyond the borders of Reality and found knowledge that drove him to rebel against his Master and/or Creator? Perhaps he acquired some dark powers in the Outside? Did his nature change or did he fulfill his purpose? Or are they even the same being (we know one can be two...)?
The Dragons (like Ferrovax) also are hard to place. They are clearly high level cosmic beings, and had important jobs in the early days of creation (described as geological movements etc). So where do they fit in?
In my opinion, it was always obvious that TWG and the Outsiders/Old Ones were linked. By definition - TWG (as Creator) came before Creation, so must have come from "Outside" of it. That would imply some level of bond - even if distant - to the Outsiders. Garth Nix's Keys to the Kingdom series touches on this, with the Architect (creator) coming from "Nothing" (a similar concept to Chaos/Outside) and being a type (perhaps the first type) of Nithling (Nix's version of Outsiders). Nix never does go into why no other similarly powerful being then emerged after, however.
What will be interesting to see is whether any other Outsider Lords/Old Ones are of similar power to TWG, and why TWG chose to break away - even if it was just pure instinct. In a strange way, it reminds me of the Warhammer 40k Chaos God Malice/Malal, who represented Chaos' nature to turn against itself.
