I see, thanks for the clarification.
So for systems beyond 1D, the approach I outlined of keeping the various degrees of freedom (dof) separate within the site set (array of site Indices) is typically superior in many respects. Not only will MPS algorithms, such as DMRG or TEBD, run faster but it's also easier to code in a generic way. In ITensor, you can make 2D systems or systems with a mixture of different types of dof by just filling an array of Index objects with the sites you want to have.
So I guess I would ask a question back to you of what advantage you anticipate by making a larger Index that represents two or more dof? Is it code which is more generic or easier to write? Or better performance of a certain algorithm such as DMRG?