For most of the buildings from communism era - all the utilities run through the apartments anyway and there is absolutely no place or way to retrofit these utilities without extensively either re-doing it from scratch, or trying to somehow retrofit it on the outside.
All of these options are a non-starter considering basic AC starts from $500. Why should anyone invest more than that?
Permissions and structural concerns aside, you only need one 65mm/2.5" hole in the wall to run the high/low pressure gas lines, a drain hose, and a power cable, plus couple more non-penetrating drill holes on the wall to mount the inside and outside units. You'll need a hole saw attachment on a drill, a vacuum pump to thoroughly dry out the system, and bits of plastic putty to fill the hole against intrusion. It's a less than 5 man-hour job.
you don't really need drain hose for outside multisplit unit, my AC drain hoses from all indoor units are connected to my WC tank, I used previously pumps to push the water to the roof, but they were not reliable and once after thunderstorm they died when I finally went for passive solution, should have done it from the beginning)
Many communist-era buildings had a service shaft the width of the back wall of the toilet closet (yes, bathroom and toilet are separate rooms). This was hidden from everyday view with large cabinet doors.
A national-scale project can likely package cooling for these shafts, possibly emanating from rooftop units.
All of these options are a non-starter considering basic AC starts from $500. Why should anyone invest more than that?