Ok there is 5,280 feet in one mile. Confirmed by Lostpedia Naomi said the plane was found in a trench 4 miles deep which means the plane is about 21,120 feet deep. Using the link below you will find a company which has built a vessel capable of diving depths over 20,000 deep and able to fit 3 people in it. I copied a paragraph for those who do not wish to read the whole article.
Link
Deep Ocean Expeditions
“In early 2000 he got together with Michael McDowell, an Australian entrepreneur and adventurer who is the CEO of a company called Deep Ocean Expeditions (DOE). DOE regularly charters the Russian research ship Akademik Mistivlav Keldysh and its two Mir submersibles of offer tourist dives to famous places on the seafloor of the world ocean. At 6,500 tons, it is the world's largest oceanographic vessel while the Mirs are capable of diving with three people to depths as great as 20,000 feet. This depth capability meant that they could reach 98% of the seafloor worldwide.”
Now as far as the bodies crushing due to the ocean pressure I’m not sure, but Naomi did say something in the regards of vessels taking pictures of the bodies in the plane. Now I am assuming the bodies were in tacked. Enough so that they were able to be properly identified, which must mean they weren’t crushed but what did they use to identify them? Blood samples, teeth, bones, hair? I mean how did the others manage to replicate any of that?