From my point of view, if the difference between what about and how about in general is slight, the difference between what about you and how about you is even slighter. They are certainly interchangeable, as you mentioned, but I would go so far as to say that their common usages are semantically indistinguishable. In point of usage, Ngrams shows a slight preference for What about you: COCA ...
meaning - "What about you?" versus "How about you?" - English Language ...
Some of my colleagues have argued that when a statement/question uses the work "how", the reader expects to get a list of solutions. Examples: "How could world hunger be solved?" "How can a
The meaning of "how" in questions - English Language & Usage Stack Exchange
"How to correct this error" is a phrase that might do well as a title. "How do I correct this error" is a complete sentence.
'How to' vs. 'How do I' - English Language & Usage Stack Exchange
In my experience as a native speaker in the Middle Atlantic region, there is a slight difference. "How are you?" is a bland greeting for someone you haven't seen for a while, while "How are you doing?" spoken in full (as opposed to being shortened to "Howyadoin?") may be an actual inquiry. The latter is more common when there is some expectation that the subject might not be doing well. For ...
The first version listed ("How is it possible?") is the standard way of asking in the United States, Canada, England, Australia, etc. The second version ("How it is possible?") is how English speakers in India ask this.