I would hardly call 4GB a hefty upgrade. It's necessitated by going from a 256 bit to 320 bit bus. This is what the 3080 was going to offer before being cancelled and sticking with 10GB.
It's not going to make much difference, but it's a good move to counter the existing 4080, at least in marketing. Maybe a 4080 Ti will match the amount exactly.
Wccftech has learned from its sources that the AMD Radeon RX 7900 XT will launch with 20 GB of GDDR6 VRAM. AMD plans to launch an RX 7950 XT later with 24 GB of video memory.