Even considering this trade is ridiculous.
There is no rookie QB in this draft that will come in and light the world on fire. Rookie QBs take time, even Peyton. Not to mention each QB in this draft has at least 1 significant concern. And while you're waiting for this rookie QB to "mature", Suh passes his prime, Wake heads out the door, Pouncey gone, etc etc.....and all the young guys will be ready for the 2nd deal and taking the cap money.
Trading Tannehill means complete rebuild. You might as well blow it up and start over (which make no sense after trading for Quinn). And if so, i doubt Gase makes it through the entire thing.