There seems to be a couple of projects in the works.
- There's a beta of a Gherkin editor here: http://gherkineditor.codeplex.com/ (windows)
- Cucumber's author has created a web-based gherkin editor (relies on javascript, Ace and Node.js). Perhaps a bit more complicated to set up, but it could be integrated into a CMS or other web-based system.
Neither really substitutes for a conversation with your business domain experts.
