Here is a suggestion for a solution/modification of Daptiv to make this work. Allow an user to be applied at a specific % of their capacity to a given resource type/role with the total not permitted to exceed 100%. For example, John is a Designer who is budgeted to support BizA, BizB and BizC (or organization, vertical, etc.), for simplicity at a 30%, 30%, 30% (10% for admin/overhead). Then, Designer resource type/role could be set as Designer_BizA, Designer_BizB and Designer_BizC. John (or any designer) could then be assigned a % to support each role (thus the businesses/verticals), in this case 30%, 30% and 30%. This would then reflect properly in the Capacity Planner since John's capacity is properly divided into the specific role hie is playing for each business.
Does this make sense? Don't know how difficult that would be to implement but it would reflect the reality of how shared service organizations budget capacity and allocate resources. The default would be 100% but there are many instance in which resources are divided.