2 discs???? You DO realise you can fit around 6 Gigabyte on a PS2 DVD. Making it 2 discs would make it the biggest game ever made. Don't be so crazy! ...
(Although...)
Going back to the thirties would make it just like Mafia really, (Which I thought kinda sucked) and going into the future will probably make things less satiasfying. Laser guns? Not for me mate.
I say stick to the present and expand on that for now. No point in ruining a good formula. If it's worked before...