Ask HN: How and in what to specialize to become consultant?

Recently, I was thinking about how to become a consultant. I don't know anyone who is a consultant, I've only read about these guys here and in some other entrepreneurial-is forums. In theory, I know that I have to specialize and acquire fairly advanced skill(s) in something that is somewhat a niche but at the same time relatively widely used in order to have consulting gigs at all. Here, I'm seeking advice about the technical skills aspect, not the 'soft' skills.

A little background:

* 30 y old

* 10 y of professional experience (in chronological order):

  * 4 y desktop CAD application development (C++, graphics, Windows)

  * 1.5 y embedded game development (C, graphics, networking, Linux)

  * 3 y game development (C++, graphics, game consoles)

  * 1 y web development (PHP, JavaScript, C)

I'm looking for advice in what to specialize, that is considering the following factors:

* My professional interests: I'm quite interested in high performance sites/apps. I've planned in the next couple of months to read and go though a couple of seminal books for websites performance, starting with the front-end (Stanford CS193H by Steve Souders), then moving to the backend (with a couple MySQL performance books), going through the 'classic' webservers (for instance, there is a book about writing Apache modules in C) and into the heart of the C10K problem and solutions, in the meantime strengthening my network programming skills by going through the Steven's Unix and network programming classics, also parallel/threaded server programming. I've planned a course about distributed computing (by reading the online resources by the schedule + the textbook).

* The unknown to me: what is the most appropriate to specialize considering my past experience, my current interests, and last but not least - what skills/expertise is actually in demand for consulting/contracting in the area defined by the above.

I hope that I was clear, thanks for your time reading.