It's a mystery to me why graphics cards have hardwired RAM. For CPUs/motherboards RAM has been extensible for decades.
To me is a mystery that CPUs/motherboards still have extensible RAM, integrated RAM (if you don't skimp and go for cheap RAM) can be very fast - for example the Steam Deck has quad-channel 5500 MT/s LPDDR5, very console-like.
You're forced to make everything slower to make things consistent.
That being said, a more optimized connector, board layout and form factor could make large-capacity, lower-latency modules possible. Not sure for example if there is anything out there besides the Dell proposed CAMM form factor, and I don't remember that one being specifically promoted as "faster", mostly "smaller".