My 2013 assumption is based on Rockstar's previous marketing campaigns. Its safe the difference between the date they announce something and the actual release date will be well over a year. They had just the teaser site for Gta4 up for what, 2 years+?
Between SA and Vice City, IMO the smaller one is more likely. That or they may use only one city from San Andreas. I don't think current gen conslols will be able to run an updated version of SA.