Ask HN: Alternative revenue models for search engines?

Search has evolved significantly in the last couple of years and paid search seems to have become a viable business model in addition to advertising based business models.

Yet, there seems to be very limited exploration of alternative revenue models such as bundling search with other (paid) features or products. We are building a curated search engine for startups (https://www.symonda.com) and we want to better understand why this is the case.

Why is there limited innovation in search revenue models and what do you think the future revenue models for custom/curated search engines are?