Power Sources: The 6th Attribute?

I've been giving some thought to how TNP compares to D&D, as it pertains to skills.

If you think about how skills work in 3.x, 4e, or 5e D&D (the versions I'm personally familiar with) there are two main components: ability score modifiers, and skill points/skill training/skill proficiency, respectively. In TNP, skills are linked thematically along two vectors (Attributes, and Skillsets) whereas in D&D skills only share ability modifiers in common, whereas the remaining skill math varies completely independently; the exception to this would be skill synergies in 3.x, where 5 points in [skill X] provides a +2 bonus to [skill Y].

That all being said, where TNP veers off from this structure is with Knowledge skills. Where D&D uses INT (and sometimes WIS) for its knowledge skills, TNP instead keys them to Power Sources: Arcane, Divine, Martial, Primal, and Shadow. But with TNP having only 5 attributes instead of 6, I've been starting to wonder (particularly in the context of the sequel mechanics) could power sources be treated as a "6th attribute" for your character? (i.e. 5 universal stats and 1 variable one, rather than 6 that are universal.)

The quirk with knowledge skills in TNP is that they are grouped together, like a skillset (sort of) but they lack that 2nd vector linking them to anything else... aside from other power sources; each power source consists of one unique skill, and 2 other skills that are each shared with different power sources. Coming back to sequel mechanics in particular, with the core skills having both an attribute bonus and a skillset bonus to their dice pool, how would you do something similar with knowledge skills? My first thought was that since in TNP, all classes basically have 2 power sources, you could just... do that again. The problem is not all power sources overlap with each other, and unique knowledge skills don't overlap at all; in short, the extra math has to come from somewhere.

So should power sources be linked to skillsets? There's some synergy between the two in TNP, so maybe power source and skillset could be the two vectors linking knowledge skills together. For example, with Infiltration linked to the Shadow power source, a +2 Infiltration skillset bonus could be applied to Streetwise, Dungeoneering, and Local knowledge skill checks. Because of unique skills being their own thing, it seems that power sources would need their own bonus -- but then you end up with all skills in that "set" having the same bonus. However, if it is assumed that all characters have two power sources (say, one with a +2 and one with a +1 bonus) that could at least give the shared knowledge skills some variance. The issue with that being, now we're talking about a "7th attribute" and not just a 6th.

I came into this talking point from a place of trying to cram knowledge skills back into an "ability score" framework, after TNP successfully extracted them from that. And I feel like I'm not any closer to solving that puzzle. It doesn't make sense to give all knowledge skills a flat bonus, but it also doesn't seem to make sense giving all knowledge skills within one power source the same bonus; it seems like the more "a la carte" approach of TNP is all that works. We'll have to see how thing go, as the design process carries on.

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I've got one more post planned for May, so check back by the end of the month for that.