I think the 6090 will be less than the 5090 at release.
This time around we're getting a new (smaller, cheaper) manufacturing process, new architecture. This will allow the die to be (much) smaller.
They won't have to release a 600W complicated heavy card. They can release a ~350W card with 16/24GB that will slightly outperform the 5090 in traditional rasterization and significantly outperform it in overall DLSS gaming due to software locked new DLSS modes etc.
Enhanced memory compression tech/software will also mean 16GB/24GB will be adequate for gaming and will drive costs down.
At least that's what I hope. I don't want to see a £3k 6090FE