I just got Noelle C4 today.. 
is time to build my next tank for L12 Abyss..

Chongyun Elemental Skill(E) will overwrite Keqing's physical/electro damage, causing her Physical/Electro DMG goblet bonus useless. Whereas Kaeya's E and Q can be more easy and precise to proc superconduct, without interfering with Keqing's physical/electro atks.

hmm i dont have a keqing to test this out, but I believe their own element has priority. Like if you use both Chongyun and Keqing's elemental skills, Keqing will still do electro damage.

Although I could be wrong, in the case of hutao and xiao its specifically written "cannot be overridden by any other elemental infusion." but keqing does not have this.

but nevertheless, its still doesn't benefit keqing in anyway to have cryo damage in her blade. Unless you running meme cryo build keqing

It hurts almost every non-cryo characters - because of split damage. I cannot think of anyone else who would benefit from it normally other than Kaeya.

What I meant by the meme build was building Keqing for cryo with a cryo cup and 4pcs blizzard set. Pair cryo keqing with chongyun and xingqiu, you get a perma freeze comp that benefits from the blizzard set. So you can go full crit damage with minimal crit rate.

fischl is not affected by it since she is a range character, chongyun's E only affects melee characters.

I did use him with diluc initially, but after awhile I realize chongyun is hurting his dps more than it helps him.

To melt you had to weave normal atk in between, but diluc's ult also infuses pyro element - which makes his attacks much stronger so you'll never want to use normal atk in the first place and thanks to his low ult cost, he'll be ult-ing off cooldowns so basically you'll have a permanent pyro infused blade which makes chongyun kinda pointless in diluc's team.

The other thing is how elements are setup in this game. Because pyro triggered melt will remove cryo in one hit, no cryo characters are able to keep up with how fast diluc applies pyro. So a diluc carry melt comp is actually pretty hard to sustain.

If you wanna maximize diluc's damage, pair him with xingqiu instead. Xingqiu is capable of applying hydro quickly while being off-field and a pyro triggered vaporize will take a few pyro hits before removing the hydro effect, making it possible for diluc to vaporize all of his pyro hits.

A non-c6 bennett however can benefit from chongyun's E since he has to use normal atk in between his E cooldowns. So you get that big melt dmg.
Yup, this is where he shines. chongyun is very good with perma freeze comp. Its the only one that can sustain it well with xingqiu. Hence why he works really nicely with kaeya. You can change kaeya's normal atk to cryo, so he's no longer split damage, but a full cryo damage dealer - benefiting from the goblet fully. This build is one of the reason why I'm hyped for Ayaka, because she can pull this off.

Its because pyro triggered melt is 2x damage, while pyro triggered vape is 1.5x only. The difference is overall dps since you can only melt once on the first hit, but you can vape every single hit so you get 1.5x damage for every hit instead of just 2x on the first hit.

Its sort of system to balance the reactions, those 2x damage like melt and vape has special mechanism

using pyro to trigger melt gives you 2x damage, but removes the cryo instantly
using cryo to trigger melt gives you 1.5x damage, but the pyro remains so you can melt a few times more

same thing for vape

using hydro to trigger vape gives you 2x damage, but removes the pyro instantly
using pyro to trigger vape gives you 1.5x damage, but the hydro remains so you can vape a few times more

Inside Chongyun AOE, Keqing normal attack is infused with cryo. Which is her main source of damage. In this case her Q is mainly use to dodge deadly attacks.

There's a build alright for Cryo Keqing. There's also a build for Pyro Keqing using Bennet. I'm not surprised if Keqing can main all 7 elements with help from other characters in the future. After all, you only need to change the artifacts set.
That's because Diluc skills explicitly states that the pyro infusion cannot be overwritten by any other element.

because the infused pyro, just like the infused cyro of chong yun.

C6 Bennet makes him less powerful to pair with other element who uses normal attack, but if you dont use normal attack inside of his ulti...then its good. if pair with pyro main dps, the extra 15% pyro dmg bonus and also the infused pyro.... maybe its good. they say its bad because bennet is god tier support can go with anyone, C6 makes him ultra good to pyro dps... and the down side is that some of the build cant be good anymore, like the upcoming eula... so C6 seems to limit bennet back into a bit situational support.