Merge's development of Custom Objects for Salesforce, HubSpot, and Zendesk Sell through their Unified API addresses customer needs for customized data models, despite the complexities involved in unifying diverse CRM systems. The project, led by Prannoiy Chandran and Joshua Learn, involved extensive design specifications, engineering challenges, and customer testing to ensure the API is both flexible and broadly applicable. The initial feature set supports core data models like Custom Object records and associations, providing scalability for numerous integrations. While currently supporting a few CRM platforms, future plans include expansion to systems like ActiveCampaign and Microsoft Dynamics, with potential enhancements to the API's visual aspects based on user demand. The ongoing effort to refine and expand the feature underscores Merge's commitment to facilitating complex CRM integrations for its clients.