There are mods in development using the current GTA IV game engines and graphics and such to re-create GTA 3, Vice City and San Andreas. Rockstar aren't going to do it themselves but the modding community is out there brehs.
I remember when I started playing gta3 these communities popped up and promised to make the next big town etc.
None of them made shyt. Its too much of a hard work, especially for free.