It probably won't be some massive increase in gaming, Nvidia is not likely to jump to much more advanced transistors, just to make the same basic thing, but bigger. Most RTX 4090s were bought as entry-level workstation cards for AI workloads and Nvidia knows it. A lot of people were paying $1800 for a gaming card to avoid paying $3500 for a workstation that performed close enough. So there's a good chance the RTX 5090 is not designed for gaming. Although the RTX 4090 also wasn't really meant for home gamers, but non-sponsored people still bought them apparently, so who knows.
Although there's always still a chance Nvidia severely nerfs the 5090's AI to stop from eating themselves out of their own market. They've always limited compute performance, started limiting hash rates for crypto back when people cared about that, so why not artificially nerf AI? The bump in memory would only be useful for AI, though.
I expect the price of the new cards to scale linearly with performance again, if not a bit worse. So maybe well get a card that games 15% better than a 4090, but at 20% higher prices and probably >20% higher power consumption. Unless they don't nerf AI, then the price jump could be a lot more. Nvidia wants their $3500 from these people.