I'm going to talk in terms of controls for consoles since any player character controls there are will have to fit onto a controller.

In Oblivion we could block (LT), attack (RT), and cast (RB). Its been confirmed that blocking will now be activated by holding both triggers. Its also confirmed we will no longer be able cast in addition to the actions mapped to our right and left hands. My point being that the RB and LT are now freed up.

Considering this, imagine equipping a 1h + shield. RT will probably still be attack, LT will most likely perform a shield bash, and LT+RT will control blocking. So what of the right bumper? It is entirely possible that it has some function completely removed from whatever you have equipped in your right hand but it could also mean that your 1h weapon has some secondary action. Pure speculation but maybe that 1h weapon will slash with the trigger and thrust with the bumper...

If secondary attacks are indeed in (and that is a big if), then what about duel wielding? If the RB controls the secondary action of your right hand then the logical next step would be that the LB controls the secondary action of your left hand. Since we can no longer block without a shield equipped (correct me if I'm wrong) there is also the possibility for actions mapped to LT+RT besides blocking. This could mean we have a total of 5 different commands to attack with (RT, LT, RB, LB, RT+LT) Add this in with holding triggers and direction of movement, both included in Oblivion, and the combat is starting to look pretty dynamic.

Since we can't block with 2h weapons we can at least assume that they will have some other action mapped the the LT even if all this proves to be false.

This could mean spells are cast on touch or fired depending on whether you use the trigger or the bumper. It could mean that there are special combo moves when dual wielding (spells/2h/whatever) and both the RT and LT are pulled. The door is wide open for any number of potential uses.

So, how do you guys think they will handle combat controls? Also, if I am mistaken in any of my assumptions about what we know of controls so far please feel free to call me out.

I think you are mostly correct in your assessment. However, I would guess that the former cast button will now be used to initiate dragon shouts. Also, I bet you'll be able to block no matter what you have equipped. The only hiccup I see in that is the issue of dual casting spells. In the trailer there is a scene where we see a two handed spell being cast. We really have no idea whether or not the spell was equipped in both hands though. If we do see combinations of spells as such then I would venture to guess that LT+RT would cast the combined spell

Edit: Expanding ideas

Dragon Shout button is R3 on PS3. In Oblivion, that button switched between first/third person.

For pc (as I don't know xbox controls) going by defaults I would think this would be the combat controls

C for Dragonshouts

LMB for left hand, RMB for right hand. If you have a shield in your left hand you tap LMB for block, hold for shield bash. Dual wielders/2h users would have to tap both.

Is this confirmed somewhere?

You're probably right about the dragon shouts but that seems like a bit of a waste. Its been confirmed that dragon shouts have cool downs and there are only 20 of them that are collected throughout the game. To have a button dedicated to them right out of the sewer gate seems pretty boring to me given we may start out with only one shout or even none at all. They also seem to have pretty specific uses and we would be swapping them out a lot.

Edit: I am almost positive I read in an article somewhere that pulling both triggers performed block. Which would make sense since you can equip a shield in either hand but it is required to perform a block. It could work either way but I pretty sure its confirmed both triggers. I'll try to find the quote.

Yes, in the Game Informer Dragon Shouts article.

To be honest, all I want to be able to do is block with a one-handed weapon. Since I'll be running around with a shortsword and a spell in the other hand, can't Bethesda please just allow me to block with the shortsword? Especially as I'm on PC, and there are PLENTY of buttons that can be used for the function.
Otherwise, it'd be incredibly lame. :/