Look, we've had this discussion already. Desktop, notebook, and eventually console GPU architectures moved away from mixed pixel shader rendering precision many years ago (since G80 times) because they were architected in a way such that there were no performance advantages in using lower pixel shader rendering precision. Mobile GPU architectures could be architected the same way too, but in ImgTech's case they haven't yet made FP32 ALU's an equal class citizen because they tend to include subtantially more FP16 ALU's than FP32 ALU's even in top of the line designs such as GX6650. Obviously they have their own reasons for doing that, and not everyone agrees with that approach (including Anandtech), but it is what it is.
You have got it backwards. It is not a case of FP32 catching up to FP16, it is FP16 capabilities being enhanced. It is happening in PC graphics as well, witness AMDs Tonga and where Intel is going since Gen8.
The reasons have been given before. All else being equal, FP16 operations take less power, requires less internal (and external) bandwidth, the hardware takes much less die area which for a given level of performance which lowers cost and improves yield which lowers cost again. Alternatively, for a given budget of die space and power draw, FP16 yields much better performance. Routinely using a compact numerical representation and only using larger formats when actually needed simply makes sense. Why waste limited resources?
I would contend, and recent developments in PC graphics space agrees, that rather than mobile graphics slavishly following in the footsteps of designs targeting high-end desktop PC/HPC, PC graphics will actually be more influenced by mobile solutions. Personal computing is moving to higher pixel densities (making small errors perceptually irrelevant) and laptops are moving towards lighter designs with longer battery lives, increasing demands on power efficiency. So rather than mobile loosing their constraints and being more enthusiast desktop like (SLI! Crossfire! 1200W PSUs!) which is a ridiculous notion, what is actually happening is that the bulk of personal computing is moving towards mobile constraints.
(Indeed, many who aren't emotionally rooted in PC space would contend that mobile is where the bulk of personal computing takes place these days. Windows PCs have become a (large) computing niche.)
If we project forward, these trends don't seem likely to turn around. New silicon tech is unlikely to make compromises unnecessary, rather the lithographic challenges going forward are increasing. If you want development to move forward, regardless of whether you are a tech hungry consumer, or a manufacturer who needs new stuff to sell, being ever more intelligent about how you use available resources seems like a very good idea.