Are there any non-bureaucratic hurdles preventing more widespread adoption of synthetic vision? Occasionally, a flight will encounter bad enough weather that the crew will become disoriented. While tools like a terrain radar, ILS, and GPWS/TAWS do help the pilots regain orientation, they're not universal; some aircraft aren't equipped with terrain radar, ILS only works on approach to runways supporting ILS, and GPWS is pretty coarse and primarily aural, not visual (beyond a flashing warning sign) on most aircraft. This means that there's still a risk of overshooting or undershooting a runway, or even controlled flight into terrain.

Some higher-end private aircraft have started incorporating decked-out glass cockpits which, among others, can include synthetic vision systems -- these can show terrain, glide slopes, and other traditionally VFR elements which can otherwise be invisible during night flying or in poor weather.

I haven't seen high adoption of these kinds of systems even in brand-new airlines, though; is there a technical reason why these aren't being included (or even mandated) above a certain type rating? Is it purely pragmatism while the system becomes more ironed out? Or are the hurdles before adoption purely bureaucratic at this point?
It's not bureaucracy in the sense of pointless red tape, it's the demands of certification for brand new systems on Transport Category airplanes.  The hoops that have to be jumped through are epic. Engineering standards, testing this, testing that, covering every conceivable possibility (or trying to).

You always see new innovations in GA, then Corporate, then Transport, because that's the certification difficulty ladder imposed by the demands of having to achieve near perfect safety with a better than one in a billion risk of a catastrophic crash due to a component failure.  (Airliners are, by a far, far margin, the safest way to get form A to B aside from an ox cart - there hasn't been a crash of a heavy in the US in, what, almost 20 years now?)