If you look at GTA's "Big 3" cities (Liberty City, Los Santos, and Vice City), you'll notice that Vice City has yet to make an appearance in the HD Universe. Why do you think Vice City has been neglected so far? Do you expect the city to make an HD appearance? Discuss.
My theory is that it has to do with Miami's history in real life. During the 1980's, drug activity was huge, and it caused an economic boom for the city of Miami. Luxury car dealerships, hotels, nightclubs, etc were popping up overnight. As a result, Miami was at the front line when it came to world class. But by the 2000's, the United States government was cracking down on drug imports/exports, causing Miami's economy to slow. By then, Miami lost its relevance as a well-known world class city.
The GTA franchise most likely followed this history during the transition from the 3D Universe to the HD Universe. In terms of contemporary culture, Miami was falling behind rival GTA-inspiration cities New York and Los Angeles, and Rockstar was focusing their eyes on those two cities instead. If GTA IV and GTA V (especially Online) are any indication, Rockstar is going to want the franchise to stay modern. Another Vice City game could mean going back to the 1980's which would limit the types of vehicles Rockstar could put into the game as part of any future updates.