Here's the thing. The main reason I think LV is possible os because of the codes with Trevor and Casinos Casinos the past year or two. It looks implied that it's not just one Casino. I think Fun posted a picture of another Casino in LS besides the one near the hills.
It's not easy to simply add San Fierro and Las Venturas into the game.
I'm just wondering how Rockstar could make such a big emphasis on gambling culture and not include the most iconic place for just that; Las Venturas. There's also some cut content in the game files of the Police scanner saying "Ventura County".
If other parts of San Andreas don't even make an involvement, then don't expect it ever coming to a next installment.