Thank goodness I have been meticulously keeping track of what I've learned in Org mode for years. I've just gotta dredge that old database for some blog posts (starting with why folks who are similar to me should really consider not going to grad school...).
EDIT - sorry, I missed the fact that we are talking about producing a blog as a proof that I understand and think about programming in a certain way (e.g. as useful to people evaluating me)... You are absolutely right, then, and I withdraw my objection.
I am not currently looking for work but if I were, I think a blog focused on dev would be more valuable than my collection of half-baked github repos. Food for thought.
One also has to consider the time cost of doing a PhD, and whether spending the equivalent time working would have gotten them further not only in career, but also salary. Between a) people who go from undergrad to a job and don't really keep pushing themselves, b) people who go to grad school to hopefully skip to a more interesting job post-PhD, and c) people who go from undergrad to a job but really push hard to learn new skills (e.g. presenting at conferences, blogging about it, etc), option C is generally leaps and bounds ahead of the other two.
A PhD is worth considering if the thing you're interested in most is not really used widely in industry (perhaps some PL stuff?).
Also, prospective PhD students need to consider that there is a very asymmetric relationship between advisor / advisee compared to a normal job. If my job starts treating me like dirt, I can tell them to shove it and quit ASAP because I know that my skills can get me another job in short order. With a PhD, it is almost impossible to quit a PhD and then pick it up again if you and your advisor have some sort of falling out; every future PhD position will look at the prior "failure" with suspicion, losing the nuance of issues besides the actual work that triggered the separation.
Basically you need to really understand why you want a PhD (and whether you could do better towards your ultimate career goal without it), and if that's a "yes" you need to really make sure you can get along with your advisor for years. A strong advisor can "compensate" for a weak student (i.e. get them through the program), and a strong student can compensate for a weak advisor (e.g. students who basically do their own thing from the get go, and have high-ranking perpetually absentee advisors who do more research bureaucracy than research and advise by way of ominous single-word emails), but if both are weak it's a recipe for disaster, and only the student gets hurt.
Getting a visa into a country via graduate studies is definitely a good reason (especially in the US it seems), but often an MS is sufficient (except if one tries to get in on the green-card fast-track via the O1 visa, which requires an exceptional PhD track record).