Anyone think it would be possible for a mod to add new games to the casinos besides the three existing ones, like poker or craps or multiple varieties of slot machine?

It'd be interesting, not sure if its possible. Heck, I'd settle for a mod that changes gambling to be less luck biased.

No, because they are hard coded in. The best you could do is simulate through message boxes and a lot of scripting.

If were lucky and Obsidian has the will, the dlc will add in some new casino games, but who knows