What would happen if Amazon or some other big tech firm really did put 50,000 tech jobs over the Amtrak yard or the Navy Yard? It would be a great thing for the region, in time. But in the short term, it would be pretty disruptive for the few dominant institutions with national interests that are still based here. Comcast engineers and Penn administrators would apply for Amazon jobs, driving up skilled-labor costs. The surge of residents would drive up housing costs, adding to the recruitment burden and maybe threatening entrenched political constituencies in a couple of Council districts.