Complex initial agreements are a bad sign and suggest a lack of proper focus on how to achieve growth and share success. But if you are getting pushed in this direction, make sure the same agreement (ownership reflects performance) applies to non-technical founders as well. Document the obligations of your cofounders while you build the product, and establish ways to determine if they have met their goals. The point is not to be the only member of the founding team held to performance standards.

If the company cannot move forward until a technical product exists, you are investing in the company at a much earlier and riskier stage, since in addition to bearing product risk (will it work) and market risk (will it sell), you are also holding team risk (are your cofounders productive) and legal risk (if they bail, will you be sued for salvaging your investment as necessary).

Higher risk should translate into higher pay/equity. Don't let anyone negotiate your ownership down on any basis other than that their own disproportionately large contribution to the company (i.e. cash investment).