To put my money where my mouth is . . . .
As was stated in the articles introduction, none of these are new variants to D&D, all have appeared before in one for or another in previous editions. The article is just taking some popular variants and tweaking them to fit 5E. Which, to me, isn't all that different from taking a monster or some other crunchy bit from classic D&D and updating it to the current edition. It's a useful article that, like everything, won't be to everyone's tastes. D&D isn't (nor should be) designed for YOU (the individual) but rather US (the collective) . . . so who really cares if this article isn't tasty for you?
I've messed around with the "Players Make All the Roles" variant in the past, and like the idea . . . but when I was DMing (3E) and giving this one a spin, my player's didn't really care for it. They were game to try it, and intellectually bought into the idea, but it didn't "feel right" to them . . . I think it was just to different from convention for my group who just wanted to relax on the weekends and play their favorite game that had been a huge part of their lives (on and off) for so many years. It's funny, the few times we messed around with games that had this sort of idea baked in, nobody seemed to have a problem with it! D&D was our comfort food, and if you seasoned it only slightly different, it felt "wrong". Probably won't try it again for that reason, but I'm glad it's been added to the 5E canon of variant rules.
The "Vitality" variant is another one I like in concept and played around with in the past, but didn't end up sticking with. I played around with the 3E version of this variant, and I seem to remember first seeing it in BECMI D&D . . . if I'm remembering that properly. It reminds me of another BECMI variant I liked in theory but became too much additional work, the "Armor Value" variant (see footnote). Both rules variants address areas of the game many players have a hard time abstracting, but don't really make the game more realistic and add more bookwork. But I like the basic ideas well enough I'll probably experiment with these two rules variants again, maybe.
The "Custom Alignments" variant is pretty simple, but well written and a good reminder (or revelation) to those stuck on classic D&D alignments. It reminded a previous poster of Dark Sun, it reminded me of BECMI D&D (again) and Mystara! Classic BECMI D&D did not have the "good vs. evil" alignment duality, but did have "law vs. chaos" duality. Later as the "core" BECMI setting, Mystara, was developed, "law vs. chaos" was conflated with "integration vs. entropy", which is basically the life/death, preservation/destruction axis in slightly different terms. I've been toying around with my own Mystara 5E conversion, and if I ever get serious about it I might just use this variant.
*Footnote: Armor Value Variant -- the idea of "armor value" from one of the BECMI D&D supplements (one of the gazetteers, don't remember which one), basically splits the concept of Armor Class into two separate scores. Armor Class becomes how difficult you are to HIT, whilst Armor Value is how difficult you are to DAMAGE. So, you lose armor bonuses to your AC, thus becoming easier to hit. You gain AV based on the armor you wear (or your naturally tough hide), which acts like DR (damage reduction), therefore making you harder to hurt. Combats tended to take longer, and not just because of the additional record keeping, as hit points decreased (for both monsters and PCs) at a slower rate, despite the higher rate of "hits".