AMD has built some consumer GPUs in the recent past with HBM - RX Vega and Radeon VII (although I assume not all "HBM" is created equal).

Isn't their APU also capable of doing HBM? There was an Intel AMD hybrid chip that used unified a while back too.

That was not unified. It was just on same package. Functionally it was like if you had a dedicated gpu.

My vega 56 still has 400gb/s of memory which is still insane for how old the card is.

AMD's Hawaii architecture had 320GB/s on a 512b GDDR5 bus in 2013.

The Fiji XT architecture after it had 512GB/S on a 4096b HBM bus in 2015.

The Vega architecture did have 400GB/s or so in 2017, which was a bit of a downgrade.