Department integration costs immeadiately come to my mind.
Think of all the new office space they will need, man hours and personell to handle this and that related to mergers, new software, new hardware, new signage, new business cards...the list goes on.

What's the cost/benefit to these proposals strategically versus tactically?

In my company, attempting to consolidate multiple seperately operating entities and trying to make them become one homogenous functioning unit has been realized as a totally futile effort.