リリースノートでの発表はまだですが、取引先などサポートされるようになるみたいです。
Change Sales Path To 'Path' And Extend To All Objects - Ideas - Salesforce Trailblazer Community
In the Spring '18 Release:
Path support for Account, Campaign, and Case Object.
Path support for all picklist on Standard Objects that are path enabled. For example, you will be able to configure a path using a custom picklist field on the Opportunity object.