Could it be that smart light fixtures are the future and not smart switches? At least for retrofits?
I fear that my answer will lend itself to opinion, and the question you asked is definitely written so that you are asking for an opinion, but given some important facts, and assumptions you made that are at least in part mistakes; perhaps this will help:


  In my house built around ~1970 all ceiling lamps are wired in a way
  where neutral wire is in light fixture's electrical box and the wall
  light switches do not have a neutral


Unfortunately, this is true for many many many residences, and fortunately; is no longer allowed. This is written in article 404 of the 2011 NEC.


  If I understand correctly, then somewhat newer houses built around
  ~1990 are wired the opposite way where light fixtures do not have
  neutral, but the light switches have neutral.


This is not true. A light fixture has to have a neutral. Any circuit in existance needs the supply and return sides. Ground is a safety ground, or ... a safety neutral in essence. But it should never be used like this. If you ever see a fixture that does not have a white neutral, chances are, another wire in there is (and should be identified).

The third option you linked is just a pathing approach. This is nothing more than how electricity got form A to B to C... and most electricians wire a home with some mix of: cost efficiency, use as little copper as possible, and common sense, future expansion and smart routing.

Another thing that exists you did not mention is 3 way switches. This is a little bit more complex, but regarding neutrals, they are all present at each location inside the box.


  However, it just occurred to me that maybe the future of smart
  lighting is not smart switches, but rather smart fixtures? Especially
  for retrofits?


Have to disagree, but this in itself is an opinion. Smart switches have an advantage. They are "permanent" and separate and take the place of existing switch circuits. Not having them as you later suggest leaves you pretty much up a creek without a paddle when the IOT goes down. Having a hardwired switch has its value for sure. People buy smart outlets/fixtures, and smart bulbs, etc - but then you have one more "wall-wart" (large unsightly blob) that makes your bulb too big, or stops you from using the second plug in an outlet, or stops you from pushing that couch against the wall.


  eliminate almost all physical light switches in my house (currently I have to upgrade them to CO/ALR rated switches anyway)
  simply pull out some old aluminium wiring that runs behind walls as it would not be necessary anymore and my house will have less
  wiring in attics overall (currently I would have to trace all this
  wiring and replace splices with AlumiConns)
  still be able control my lights with help of voice, motion, phone or with a touch on smart hub screen as I would with smart switch. But
  I would not be able to have easily accessible physical switch that can
  turn it on or off.


For these points, I've adressed my answer above about value of one smart appliance over the other, but regarding aluminum... You should copper pigtail everything, you should retrofit and remove aluminum whenever the opportunity presents itself. This is a different topic from *smart switch anything. It's just smart! :)

Found this after reading Ed's note *(thanks Ed):  Simple notes on room requirements for switches
Local-mechanical means has its value. The internet is not perfect, and we all know technology is not either. But since you have a breaker, that technically is a mechanical off switch. Do you really want to have to use it?