Spy Theory 1
Was the Somerton man a spy?
I suppose the first thing we need to examine is what we mean by 'a spy'. The first thing that I think of is James Bond, but the world of secret agents, spies, and espionage is very different to what we see on the big screen. A spy is simply a person employed by a state, company or institution to obtain secret information from rival countries,organizations, or companies. In 1948 WWII may have ended but the Cold War was in full swing. Everybody it seems was spying on pretty much everybody else. The Lapstone conference was under way at the Lapstone Hotel near Glenbrook in the Blue Mountains. 110 delegates from 18 different countries, as well as all of their staff.
This was a perfect opportunity for a bit of spying by both sides. Is it possible then that the Somerton Man was working as a spy for one of Australia's enemies? (Most likely the Russians)
If so, could he have been discovered and covertly taken out?
A Russian, a certain Mr Sherbakov (no first name), was to be included in the Russian delegation at the Lapstone ECAFE conference December 1948 that was held in the Blue Mountains outside Sydney. Mr Sherbakov seems to have arrived in Australia with the delegation, but didn’t show up at the conference.
Australian Archives. “Correspondence, Reports and Statements, 1948-1955, Lapstone” Barcode 438694. page 28.
“Of the fourteen Russians who landed, twelve only have left. Apparently Sherbakov and Miss Bogotyreva are still in Australia. Mr. Brennan never saw Sherbakov during the whole of the conference and was under the impression that he had not come. (There was great uncertainty about the composition of the delegation.) Qantas passenger list received by C.I.S. some days later, clearly shows Sherbakov as a passenger.” [*]
The Lapstone ECAFE conference commenced on the Monday before the Somerton Man died. Could SM be Sherbakov? Who was Sherbakov? ~ B Deveson on Cipher Mysteries 
Miss Tatiana Bogatyreva was Soviet delegate Col. Kirrill Novikov's secretary. Col. Novokov also had nine male assistants with him. It is quite possible Mr Sherbakov was one of Col. Novikov's assistants. 
Maybe the pair decided they had had enough of Russia and decided to run off together and start a new life in Australia under assumed names.