He doesn't really look like Demise though.

So basically Demise saw a new Gerudo baby boy yet to be born and decided to take his body for himself?

This trailer seems to have mostly dispelled concerns that this would just be BOTW 1.5 or glorified DLC.
The discourse around the game has seen a marked shift for the better.

Something like that it's never fully explain, Ganondorf's mother was a Gerudo witch or to be accurate twin Gerudo witches (The Twinrovas in OOT) who were in their singular fused form when he was born it's unclear if this part of a ritual for Ganon to be reborn as a Gerudo. All we know Ganon and the Gerudo boy are and can be separate entities because in WW Ganondorf no longer has the dark beast while various other games have shown Ganon to be its own thing and even have different hosts/avatars.

They don't look very similar to me beyond some surface level similarities. Both having red hair is if course intentional but they don't look the same overall.

Ganondorf has been made to resemble Demise more and more, you posted TP's version here is the first version of Ganondorf after Demise debuted in SS.

Now TOTK.

While he retains his original design concept the changes to him since Demise was added to the canon should be noted for example pre-Demise he had short red hair only while post-Demise the hair design mimics Demise a lot closer along with the bulkier build, the surface level resemblance is intentional as one is an incarnation of the other.

It's a seemingly small addition, but enemies fighting amongst themselves is a nice touch and should help create an even more dynamic and "alive" feeling world than BOTW.

(Yes, I'm aware enemies will interact in BOTW, but TOTK highlighting it in the trailer makes it seem like this will be more emphasized this time around, as opposed to something that rarely happens)

The issue of enemy variety also seems to be significantly improved with the addition of the constructs, redeads, gleeoks, boss bokoblins, the big box golem, the new flying enemies, and the use of fused weapons/gear by enemies.