As for SSD texture cache, time will tell. It's already a game changer on pro card for offline rendering. SSD are becoming cheap and having a 1 TB added to a 600$ video card might end up to be a minor portion of the global price.
There are advantages of having it on the GPU. Lower latency. The GPU could also handle the I/O instead of the cpu and the bandwidth between the cpu and the GPU could be used for something else. The GPU could also use it to store many things like more mipmap, more level of details for geometry etc. The demo of the unreal engine 5 demonstrated what you can do by having a more detailed working set.
While having an SSD locally on the graphics card will certainly be faster than fetching it from the SSD storing the game, it will still be a couple orders of magnitude more latency than VRAM, so it still needs to be prefetched carefully. In reality it doesn't solve any problem.
While SSDs of varying quality are cheap these days*, having one on the graphics card introduces a whole host of new problems. Firstly, if this is going to be some kind of "cache" for games, when it needs to be managed somehow, and the user would probably have to go in to delete or prioritize it for various games. Secondly having it in a normal SSD and going through the RAM serves a huge benefit. You can apply a lossy compressions (probably ~10-20x), decompress it in the CPU and send the decompressed data to the GPU. This way, each large game wouldn't take up >200 GB. To do the same on the graphics card, it would require even more unnecessary dedicated hardware. A graphics card should do graphics, not everything else.
*) Be aware that most "fast" SSDs only have a tiny SLC SSD that's actually fast, and a large TLC/QLC SSD which is much slower.
And I think the fact most gaming studios use third party engine is a better thing for technology adoption than the opposite. The big engine maker have to work on getting the technology into the engine to stay competitive and the studios only have to implement it while they create theirs games.
These big universal engines leaves very little room to utilize hardware well. There are barely any games
properly written for DirectX 12 yet, how would you imagine more exotic gimmicks will end up?
Every year which passes by, these engines get more bloated. More and more generalized rendering code means less efficient rendering. The software is really lagging behind the hardware.