Honestly, I think that's a good thing, the current one is plenty of powerful for what it is. Specially considering it's a portable device where power consumption and thermals are key.
If anything, it's the games the ones that should try and adapt to more humble hardware. These days it makes no sense to increase so much the requirements for such marginal graphical difference.
A new Steam Controller on the other hand, to match the deck controls, is something that is missing.