EDIT: IT APPEARS THE CONTENT HAS BEEN PURGED FROM IMGUR. MOREOVER, HOYOVERSE HAS HIRED AN EXTERNAL COMPANY TO PURGE ALL THE LEAKS FROM THE WEB. WE HAVE BACKUPS OF THE LEAKS, BUT WE DO NOT WANT TO BRING ANY TROUBLE TO ERNEST NOR THE TEAM BEHIND KBIN. WE'LL LOOK FOR ALTERNATIVE HOSTING OPTIONS BUT FOR NOW, WE'LL KEEP THE CONTENTS OFF THE SITE.
I don't know the circumstance, but it seems that there is a leaker (or group of leakers) that has somehow obtained a large amount of directly from Hoyoverse. This data contains big leaks along with concept art of previously released characters. I've tried to compile all of it in this document, but please let me know if there's something I missed.
Shout out to r/genshin_impact_leaks and u/nlone324 for compiling the leaks in their sub.
It's possible Hoyo is working on new character models.
Character Leaks
Character design sheets
Unreleased Character Concept Art
Note: Apparently these are all the design for one single character.
Fontaine Concept Art
Early 3D models
** Fontaine Series of Weapons**
Early Designs Concept Art or Character Models
Miscellaneous