Thank you all so much for your replies. I very much appreciate all of your active participation on these forums.

I recognize the GM can nerf anything, but my group likes to always start from "rules as written" (RAW), and then introduce campaign rules to clarify or limit things. We strive to all be playing by the same set of rules when there are different GM's. But the first step on our journey is always to understand the rules as written.
With regard to the +4 augmentation cap, I don't think that would apply. I interpret the rules on page 39 as a restriction to increasing the skill itself. In other words, if I have Athletics-6, I can only have spells/gear/etc. increase my Athletics skill to a maximum increase of +4, or, in this case, Athletics-10.
However, in the case of the Weapon Focus, this adds "its Force as a dice-pool bonus on your Attack test". In other words, it is not increasing the skill itself, but that adding extra dice to the check.
Now, some have suggested that "rules as intended" (RAI) is that only specialization/expertise are allowed to exceed that +4 limit, but I always am wary of RAI arguments because they can be so hearsay and subjective.
If ultimately the +4 limit is applied, then it would logically follow to apply it to most of the other foci including Power foci, Spirit Foci, Enchanting Foci, etc. All of these are worded as adding extra dice to a check. So, then we are basically saying the maximum rating of nearly all foci is 4. That seems somewhat limiting at higher levels of play. If intended, great! I'd love to see that as an errata though.
(Oh, and just to clarify, the availability limits do not apply during character creation since these items are not illegal.)