We want to be a human friendly file. If we had a JSON or XML file, it would be too complicated for a non-developer to write or read it. On this way, I think it doesn't matter if the website is done in wordpress, drupla, static files, flash, etc. It's just a simple file.
Also, we are following the same pattern as the robots.txt file.
I would strongly suggest e.g. JSON or XML - if you can upload a website, the chance are that you could also create something like this. There would of course also be a template where absolute noobs could fill in the details and get correct output. With our current tools, implementing a clear text data storage seems like a pretty stupid idea - everyone would have to implement their own parsing. With e.g. JSON, there are libraries for every language and it has validation.
YAML, or the format used by Python's configParser or PHP's INI files (don't know what it's called), might be easiest. Less syntax and formatting.
I'm not so sure about the proposal itself, though. For local, small businesses, how much can we assume about technical ability? If they have to pay the people who did their website to keep it up to date, how can we be sure they'll use it?
Yeah I have to second this. No "non-techie" person will be updating this on their own, for the simple fact that they need to upload it after their done or edit it via ftp... etc. A wordpress plugin would help, but it still lacks great visibility to the business owner.
The main issue I see with this philosophy is that you are pushing the responsibility for understanding the format upstream, similar to all the problems people used to have with malformed RSS feeds.
If you want to have a feed of some kind that is machine-readable then you need to have a spec that is unambiguous. Using JSON or XML helps. Having a clear understanding of what could be in each field, including currencies, timezones, etc, is required.
Also, we are following the same pattern as the robots.txt file.