On the topic of fitting all of SA it would be possible, not due to compression or anything... scale is the keyword: everything must be rescaled, making all the terrain files, characters models and everything smaller in size on disk... also games can be run off of memory sticks, the only problem is securing the stick so people don’t wipe it and get a cheap stick with decent size; this can be solved in a multitude of ways; however these would require yet more of the redundant firmware updates.
You may know take into account compression which grows exponentially (quite literally as file size is all based off of base 2 [we count in base ten]) from year to year. The only sacrifices would have to be a few features, and maybe storyline length. Their may be some people out their who don't agree with my analytical views