Okay so now here is my problem with this: I can't just find whoever knows HTML/JS/CSS and get them to work on this by sending them a ZIP file with the interfaces in it. They have to install the environment and application and then iterate using this DSL, refreshing the page to see it in the browser.

It is far easier to find a really good designer, who knows HTML/CSS and a bit of JS (probably jQuery) than it is to find a really good designer, who knows HTML/CSS and a bit of JS (probably jQuery) and then is also comfortable configuring a Rails environment and also proficient enough with coding Ruby to learn quickly and without support or input, this custom DSL.

There are already so many people that have the skills you need, why force the issue? Let the technologies be what they are. In my experience, communication between team members is the single highest cost in building software. Unless you're a designer/developer or you're working with a small team on your startup and you happen to have all the skills you need right there in one office and timezone, you'll need to confront the issues of resourcing, iteration and staff changeovers - what I'm advocating is that we play to the prevailing skill separations and reduce the communication overhead.