Thanks for your answer. Kickstarter is not an option for me as I'd be required to have a US social security number. I don't have one, I'm Swiss. I'd go with Indiegogo. Crowdfunding is not my expertise at all. How would you go to spread the word about the campaign? I know my target audience doesn't lie within the pro coders crowd but rather within designers, start-up founders, people willing to make a career change and maybe CS students.
As for Rails, yes, there's a lot of magic happening but my goal would be to decompose that 'magic' to explain what really happens behind the scene as the goal would not be to teach how to copy code (like many, many online courses are doing) but rather how to write it. My main skill is C# and ASP.NET but I don't consider it either as a good starting point for a beginner.
PHP could be good as well but writing good code in PHP is very challenging for a beginner (in my opinion and experience). Also, PHP, even though it's used on loads of sites, is not a 'hot' technology anymore.
Lastly, I would like to have fun creating this course... ...and I'm having loads of fun writing Ruby!