The top to bottom phrasing is not particularly well-written, although I can see several ways that a new product range could have HBM throughout its covered range even if that range does not include every part of AMD's overall market.
Fiji has 4096 shaders and is about 600mm². One may (somewhat simplistically) suppose that on 14nm, it would be about 300mm², therefore that a 14nm semi-Fiji would be around 150mm², with 2048 shaders, just like Tahiti. With a single stack of HBM2, it would have about 256GB/s of bandwidth, which is a good bit more than Tonga but slightly less than Tahiti in its fastest variant.
So yes, I think it's reasonable to assume that AMD won't bother making a new GPU under 150mm², and probably just recycle Pitcairn—again!—and Bonaire.