I think the writer is correct that what constitutes "vitals" changes over time, but I disagree that this automatically means an increasing tendency toward liberalism. I think the PCA is actually a case in point that this simply isn't so.
When the PCA was formed in 1973, it was done under the banner of the authority of Scripture as the central and most fundamental "vital" to be subscribed to. Fair enough—but any good Baptist then or now could subscribe to that, and thus many of the PCA churches established in the early years of the denomination were quite baptistic in form and practice, if not technically in their claim of theological standards. I personally have known ruling elders ordained during that era who admitted that they had never read the Westminster Confession of Faith. It wasn't really until the union with the RPCES in 1982 that a deeper commitment to distinctively Reformed doctrines became more prominent.
Since then, if anything, the PCA has gotten arguably more theologically conservative in its self-described "vitals" and in the documents adopted as containing our positions. The position papers on divorce and remarriage, homosexuality, and the insider movement are prime examples; even the position paper on creation, while broader than some would argue is acceptable, nevertheless defined parameters that clearly excluded certain views. Meanwhile, the study committee on Federal Vision theology (which many presbyteries now ask transfers and ordinands to avow their agreement to) also laid down some clear lines. Most recently, the study committee report at the last GA on women in the church asserted in no uncertain terms that there is no exegetical or ecclesiological basis for ordaining women to an office in the church.
(In addition to this incline instead of decline, our presbyteries are still assured their right to define the terms of their own membership in our preliminary principles, and some do.)
Thus, the persistent claims of a certain segment of the PCA that we're on a slippery slope where one slight misstep will undoubtedly result in the theological downfall of the denomination, to me, seems hollow or even bitter. There is a curmudgeonly quality to the way they continue to rant about this, with another article or blog post passed around once a month or so describing how the denomination is on the verge of theological heterodoxy. The one linked above is merely the latest example.
Meanwhile, some/many from that same segment seem increasingly committed to using unsavory tactics to accomplish their goals of fear-mongering and flag-planting at the Assembly level. I experienced this first-hand two General Assemblies ago, when I served on the Committee of Commissioners for the Administrative Committee (AC). As it happened, that was the year that the AC brought forth the recommendation to form a study committee on women in the church. As the discussion proceeded, it quickly became evident to me that the flag-planting crowd had worked hard (I'm almost inclined to say they "conspired") to stack the committee with men who would oppose this action, and indeed the result was that the committee's report recommended that the assembly vote it down.
Now, how do I know that they stacked the C of C thusly? Because when it was brought to the floor then those who opposed forming that study committee were obviously a minority. Yet the C of C structure is meant to be a representative body of the denomination as a whole. One would think if that were the case then the C of C would have had a greater diversity of voices than it did.
Ironically, the same voices that frequently serve as spokesmen for this group of flag-planters are quick to fuss about any other groups they perceive as colluding to subvert the will of the assembly as a whole—most recently, a group known as the National Partnership. The flag-planters assert that their actions are different, because if they gather or communicate then they do so openly for all to see. But experiences like mine with the AC committee of commissioners seem far too coincidental for this claim to be believed.
There have always been subsets of the denomination who discuss their views and make use of connections and relationships to enhance understanding and even cooperate in advancing certain points of view. Personally I've never been a part of one—unless you count the conversations over meals or drinks that take place organically. But they exist, and always have. I'm not particularly troubled by their existence, nor do I feel threatened by the presence of those groups that I may disagree with on certain issues.
What troubles me about the linked article, others like it, and the subset group that has devoted themselves to planting their flag and trying to "take back" the denomination as a bastion of conservative, orthodox Reformed theology is two-fold.
First, as I've asserted above, I think they are simply wrong—or at least presumptively overstating the status of the PCA. I believe that most other teaching elders of the denomination similarly consider their rants and prognoses as overblown hyperbole. But as is so often the case, yelling and stomping one's foot enough will make people pay attention, and thus the average member and even many ruling elders are given over to the misimpression that the latest heated discussion—or the next one—amounts to the PCA's having stepped on a trigger of a landmine, and we are about to be blown up.
Second, it presents as uncharitable at best, and unbrotherly at worst. A friend once commented that "no one outside of the PCA accuses us of being soft on conservative theology." I think that is still true. But the reputation of the PCA is being re-defined by the petty, bitter squabbles about whether we are conservative enough, rather than by our commitments to administering the Gospel effectively. The PCA is full of amazing testimonies of how God is at work using our humble denomination as an instrument of grace, but the loudest noises coming from within our midst seem to be grumbling instead of praise.
A final comment to how some of my fellow elders have taken on an uncharitable attitude is also immediately relevant: originally I began writing this out as a (much briefer) comment to my old friend's Facebook post that linked to the article. However, the last time I wrote a comment on something this friend posted, he deleted it. The only reason I can see for doing so is that he didn't want any words opposing or questioning his position. It's his Facebook wall, and he can choose to allow what he will—but if he's not planting a flag, it seems like he might be more open to iron sharpening iron even (or especially) on matters of vital importance.