Startups globally have been pushing the boundaries of what is possible, particularly in terms of innovative revenue models. From subscription services to platform businesses, these pioneering models of income generation have placed startups at the forefront of business model innovation.

The first innovative revenue model is the 'freemium' model. This is where basic services are provided free, but users have to pay for advanced features or capabilities. It encourages more users to try the product and potentially upgrade to a paid version.

Another revolutionary model is the 'subscription' model. The Adobe Creative Cloud, for instance, moved from purchasing software outright to monthly or yearly subscriptions, providing constant updates and enhancements to their product suite.

The 'on-demand' model, powered by the advent of the gig economy, allows businesses to provide services as and when needed by customers. This model has been popularized by companies like Uber and Airbnb.

The power of the 'platform' model is also undeniable. A platform business generates revenue by facilitating exchanges between two different user groups. Tech companies like Etsy and eBay have successfully adopted this model that connects buyers and sellers.

Lastly, the 'data' model is becoming increasingly prevalent. Startups are utilizing the value of data, whether through selling it, analyzing it for insights, or leveraging it for targeted advertising.

These innovative revenue models are not without their challenges. For instance, scalability, competition, and variable income can all pose risks. Nonetheless, the flexibility and potential for high growth that these models offer make them an appealing option for many startups.

Endeavors into new revenue models have indeed established startups as vital players in the global business scene. Their continual push for the unconventional sparks a renewed sense of possibility in the world of business, proving that with innovation and ambition, the sky is truly the limit.