FinFET and HBM are, thus far according to AMD's own roadmaps slated only for their GPU range, the only known/rumored implamentation of HDM on an APU is the rumored 16 core Zen APU which does not use 3D stacked HBM but instead psuedo 2.5D staking memory off to the side of the CPU/GPU die, that rumor never came to fruition and has been completely ignored on every AMD presentation and roadmap since, suggesting strongly that the 16 core variation was either made up or a scrapped internal project.
But lets pretend it wasn't and they made them, given that the NX would likely be the first hardware to ship with them, just how much do you honestly believe AMD would sell their cutting edge APU's for?, because i'd argue that the price they would be asking for them would be easilly outside of the budget Nintendo would be willing to pay, especially since AMD would likely want Nintendo to foot part of the bill for the initial mass production costs and testing.
If Nintendo wanted HBM and FinFET in NX it would need to be seperate CPU/GPU, which is inherantly higher cost than an APU, and for the specs people are parading around lately, would mean even higher BOM for the retail unit.
Even still, faster memory would make little difference if the GPU and CPU were not powerful enough to take advantage of it, and the APU options for achieving that just arent here yet - maybe in another 3-5 years, a hack job solution would of course handle it but would introduce high price, high temperature and high power consumption.
So no, either the console is astronomically priced or they "could not".