It defeats the primary purpose of CRM. CRM is hard work to get proper adoption ... Why make it harder?
That being said ... If there are a completely different set of sales and marketing and customer service and related personnel that interact with the customer sets of the different MAS databases, then it isn't a big deal. For most organizations, it creates extra work for the front line people on top of the extra work the crm system itself imposes.
Time will fly by. My advice is wait.
Or as a secondary but not recommended approach, look into the greytrix integration.