I have no idea how this one-time payment pricing model could ever be a practical value capture mechanism. It is akin to a Ponzi scheme where new investors are paying for the support of old investors. Unless new investors are found, the merry-go-round stops. More pointedly, depending on the solution you are providing there is a most likely a target domain of users only a percentage of which you will ever reach. I don't think I want to use a SaaS with a one-time pricing model for one important reason. I want them to survive! So, I am willing to continue to pay for value. It does me no good to get a deal on something that won't work for me in the future. Of course, I may be missing the "twist", the "one quick hack" that turns a one-time pricing model into a sustainable revenue stream that allows a company to support its base, respond to changing requirements and oh, compensate the people who produce the product.

It sounds to me like this is just an obvious gimmick, designed to attract a bunch customers who pay the one-time fee in order to bootstrap a SaaS that will inevitably turn to a recurring revenue model. Good luck, you'll no doubt find some customers.