I'm sure it will have the usual, godmode, infinite ammo, infinite cash, all weapons, et cetera. But mabye in the future trainers will have the unusual options like stop time, lock wanted level, give pedestrians weapons, cars fly, etc will come if you just wait it out.
WAAAAYYYYY to early to tell. it will be at least 3-4 weeks for coding like that. Even san andreas took a month to get a good garage editor.
The problem with GTA4 is that there are no garages so a car spawner might be possible.
But something like the garage editors where you can spawn a bulletproof, damage proof car might not be possible this time around. regardless things like that will take time to work out.
I'm sure whoever made the GTA San andreas editor will make the Grand Theft Auto IV version when they get the game. but I would definitely like a large trainer for this one.
Another problem is that it use GFWL to save the game if we're not online we can't save at all (trainers don't work when using GFWL) I guess we're screwed if there's no way to save without being connected to Game for Windows Live.