First, let me reiterate the main generic arguments in the blog post. These tags do not indicate the topic of the question, they indicate its breadth or depth. They cannot work as the sole tag on a question. They are hardly any use in searches. There is no reason to subscribe to them or ignore them. Their applicability is subjective at best; at worst they highlight questions that are not suitable for a question and answers format (not constructive or too broad).
For questions that don't admit a definitive answer. Please do not ask too many of these.
Saying that a question with this tag is probably no good for the site does not bode well.
A soft question is a question (possibly subjective) about the field of theoretical computer science as opposed to being a question in theoretical computer science.
for a "broad, overall view or perspective of an issue or problem."
which comes back to “probably doesn't fit in the Q&A format”.
I can see one use for big-picture, which is to highlight questions that provide an introductory overview of a topic. But Stack Exchange already has a mechanism for that: list the question in the topic's tag wiki.
If your argument for having those tags is that they do no harm on Math and CSTheory, please keep in mind that CS is likely to have a larger programmer crowd, weened on Stack Overflow, where such tags are routinely burninated and questions such as lists of books¹ or career considerations² tend to have far worse quality and are usually closed after some conflict.
¹ Tag wiki.
² Academia, if any