[quote=Green]
I think the most obvious question would be; What is your character doing in this setting? Out of the two fan-type characters that could potentially pop up now, the space marine is the one that is the easiest to integrate into the setting. I say -integrate- because if he walks around talking about the god emperor, and how he is a space marine, and whatever, he isn't really very well integrated, now is he? (Unless his motivations become the integrator, which I suppose could remedy that, but it's jiffy.) A namekian, on the other hand, is very.. out of place. Especially if he's calling himself a namekian, from the planet namek, you know, that blue one with the green water. Personally? I think both examples should be denied if they use background information or terms that is native to the setting from which they derive. Like, saiyans, God emperor, tyranids, kamehameha. Etc. Schradinger has a very good example of how you can take a character that is based on a different canon setting, like star wars, and integrate him into a different setting without removing the core of what being that character means. In my point of view, that should be a rule of thumb. A character should adjust to the new world he enters, not the other way around.
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Isn't the whole premise of this that beings from many epochs are pretty much colliding upon a single realm/world? If so, then how is any fan-based character any more out of place than purely original ones? Save for being a character that comes from this world, which is difficult to achieve finitely seeing as little had been divulged of it. To that credit, I liked the old continuum simply for the fact that the setting was very clearly defined as to make it possible to create a character specifically for the continuum. 

Furthermore, I would contest that in terms of general abilities, the application of "Ki" translated pretty well across most universes.