If your job is the type where you're on the same team/project for years on end doing basically more of the same thing from month to month, then I can understand why you wouldn't necessarily see the value in this kind of tool.

I update mine once every 2-4 months or so, whenever I complete a project, earn a certification, take a course or work (professionally) with a new technology.

Having 10 different formats does sound a bit like overkill, but I don't think that is a reason that the OP would want to ignore or exclude any that users would find useful. Personally, I keep about 3-4 (linkedin, .doc, .pdf, .htm).

Just wanted to second this. It really depends on your velocity -- 6 month consulting gigs or 5+ year stints with a single company. After five or so years of short-term consulting for example you're looking at 20+ entries for work history alone, not counting mentionable side projects, service, other items. And you're a tech candidate so it's got to be keyword-optimized. Recruiter X wants it in MS Word, employer Y wants it in their proprietary ATS, employer Z you have direct access to the devs and can use the LaTeX "secret handshake". Then the anonymized HTML version for your blog, etc. So you get this explosion of formats and, if you edit each format manually, a quick resume update can take all day. Let alone a redesign.

Ten might be overkill, but I really want to have an html version hosted online as well as a PDF version with the same content and LaTeX-quality typesetting (my current resume is written in LaTeX). There's some hacky tools out there for taking a resume in markdown and making html + pdf, but nothing really satisfactory, so I'm thinking this might be exactly what I've been looking for.

Problem is, your CV should be optimised for the format in which you are looking at it. A Word and PDF version should be no more than 2 sides of A4, with the page break at a logical place. HTML should be interactive, with widgets that show relevant content.

Web design is fundamentally different to print design, and your CV should show that you understand that. So you should be able to make a Word version save that to PDF, then re-write and redesign the content for the web page.

In an optimal sense, I agree with you, but I don't have the skill/time/desire to make a really awesome web version as you describe, and would be quite happy with one that roughly mirrors the printable version. There's always LinkedIn too, which gives some of that interactivity.

Further, this (really the underlying JSON resume schema) could be a great starting point for a fancier web-resume generator working from the same content.

That's an opinion that not everyone holds, and doesn't necessarily hold for all sorts of people/positions. If you do design-heavy types of work, then it makes a lot of sense to heavily optimize for the format. If not, then that's just window dressing on a format that is used to convey information.

I highly interactive web-based resume for a lawyer or accountant might seem silly in that community (and some of my lawyer/account friends agree).

I'm looking forward to hacking this into apis/chrome extensions that will let me update my 10+ jobs profiles all at once.