I don't know if Nintendo is even going to Gamescom. They will more likely have hands on time with their games. Super Mario and Donkey Kong are fan favorites. Zelda: The Wind Waker is sure to put smiles on people . They don't need to show anything at Gamescom. Are just show off a new trailer of Monolith Soft X and come away unblemished. My opinion, that game looked better then everything that was at E3 (almost).

Probably some new footage of already announced games

They will have nothing. They never cared for expos other than E3 and I don't see it possibly change now that they have NDirects. The best that we expect is maybe different demos but I doubt even that will happen.

But I expect new thing from 3rd party tho... and by that I mean Sonic and maybe W101(first party published but 3rd party developed)

polkamon?

They're not going to show anything at all from "Zelda U" until next year. They are wanting the spotlight on Wind Waker HD right now, not the next original game.

I think they're likely due for another ND sometime in Sep., though I could be wrong. And honestly, the whole idea of "they have a bunch of future titles they just haven't revealed yet" is kind of a massive no brainer. That is the case for every single gaming company on earth, with the exception of small studios that literally can only work on one game at a time.

Microsoft will be doing the showing. You won't get any more showing from Sony, so why Nintendo needs too. Maybe a third party game for Sony.

I doubt they'll show anything new. Why should they anyway? They have announced enough 1st/2nd party games imo.

Just FYI - Gamescom line-up according to nintendo.de:

Wii U
•Pikmin 3
•The Wonderful 101 (Launch Aug)
•The Legend of Zelda: The Wind Waker HD (Launch 4. Oct)*
•Sonic Lost World (Launch: 18. Oct)
•Wii Party U (Launch: Oct)*
•Donkey Kong Country: Tropical Freeze (Launch: Nov)
•SUPER MARIO 3D WORLD (Launch: Dec)*
•Wii Karaoke U by JOYSOUND (eshop)
•Mario Kart 8 (Launch: Spring 2014)*

Nintendo 3DS
•Pokémon x & Y (Launch: 12. Oct)*
•Professor Layton and the Azran Legacy (Launch: 8. Nov)*
•The Legend of Zelda: A Link Between Worlds (Launch: Nov)*

*playable (maybe more, but the current Nintendo newsletter only mentions those 7 as playable games)

Perhaps they will, I have a feeling they will show Zelda for some reason.

But if they don't, it's not a big deal because the current lineup is very solid anyway.

not expecting anything at all

Maybe they will show that Pokémon teaser again.