IME, you go back to your engagement model and calculate CSM Capacity against ideal customer engagement.  How do you want to engage with the customer?  If each LoB deserves your ideal customer engagement model, then how many hours a week does that ideal engagement require related to a CSM’s Capacity?  You are constrained by the 2400-3000 minutes/week that a CSM has available.

I think you are going to find that either this account requires a dedicated CSM OR your CSM is going to be responsible for fewer named accounts in their BoB. 

You should also take into account the effort to consolidate your LoB Success Plans into an aggregated customer value conversation that rolls up to the enterprise...as well as your growth efforts as you discover new use cases and find new LoBs that want to be rolled onto the solution.

Ultimately, this needs to be a single CSM.  Continuity is key.  Being able to understand all the LoBs needs, and look across the organization from the top down is going to be key in cementing your Strategic Advisor status with leadership (different than the Trusted Advisor status you are working towards with each LoB).  If you decide to go with multiple CSMs, one is going to have to be the “Lead” to manage the Enterprise relationship.

Remember, while each LoB will have a Success Plan, you need to tie each of their plans to an Enterprise plan.  How is your solution, not only helping the LoBs achieve their goals, but how is that federated effort helping the enterprise achieve it’s goals.

Awesome discussion here, commenting to elevate this thread in the activity streams.