HUDs are around in the GA world, and they will become more common.
They were initially the preserve of the Military and prodigiously expensive, but the wonders of, what us older pilots call 'modern', technology mean that this has been simplified made reliable and affordable - for home builders, experimental, RAA and some Ga pvt types of flying but as far as becoming a 'standard' type of item we have a way to go.
Full C of A aircraft require STC to fit ( and may still be operationally restricted), or data incorporated into TCDS. STC is a very expensive option for the STC holder and would need to be researched, developed, complied, certified and munufactured under very onerous regulatory requirements for each type of aircraft applicable.
I think it is more likely that a manufacturer will do such in house for a particular type/model of their line and incorporate into the TCDS for that type. this requires will from the maufacturer and they need to be convinced that customers desire it sufficiently to order and pay for it , and it will not be cheap especially if certified for commercial IFR ops. ultimately the customer will pay, and when they are ready to do so, Cessna, or similar, will do it and then when the technology is proven reliable and accepted to be popular others will follow. the sort of thing that happened with large format PFD/MFD panels.
Yes, the technology is there and it is , in its current non-certified form, reliable (ish), but the big step into commercial IFR ops is a long way to go. integration of IR and SAR images overlaid onto the meta data of a HUD will come with that as well, but high quality images in these spectra are still relatively expensive. time and the utilization of COTS components by tech heads will bring that into the realm of the GA world sooner or later as well.
I am looking forward to my new lightweight, fuel efficient and inexpensive gas turbine engine for light/medium GA aircraft as well. RR and PWC have both promised them soon. Otherwise if you are going to OSH look for the ever present home-made jet engines on static display, that are made from vacuum cleaners and the like and ponder why we are all not using such engines now.
It won't happen overnight, but it will happen, if there is a buck in it.
HD