There's a lot to parse with this unintended leak by Micron. GDDR6X is real and not just an overclock... it switches from binary to PAM4 signaling, and while it uses less power per pin, yet Anandtech thinks it will overall consume up to 25% more power than GDDR6. But at the maximum Micron spec of 21Gbps bandwidth-per-pin, the "3090" would reach 1,008Gbps of bandwidth. Not a true 1Tbps (which is 1024) but it would be an exceptional upgrade over past NVIDIA cards. 
 
Good breakdown of PAM4 and other details https://www.anandtech.com/show/15978/micron-spills-on-gddr6x-pam4-signaling-for-higher-rates-coming-to-nvidias-rtx-3090
 
And yes, Micron uses "3090" in their spec sheet data.