Ask HN: Question about commision on ideas bought to the business.

I work for a dev company and i spend most of my time doing dev for other clients, I came up with the idea of a new service/web application and i offered it to the business, I just want a cut from the profit generated by the service. The development time will probably be split 30% in between jobs 70% personnal time. My boss doesn't want to give me a percentage or anything at this stage, he wants to discuss reward once the service is up and running if at all. Am I unreasonnable to expect this to be sorted out before hand? and how much will you expect your percentage to be in this situation?