Even a modder has made the police system better where at least they chase you and spawn totally out of site, what have we had from CDPR in almost six months.
I don't think it's really that they can't release the police system in 1.1 even, it's just it would have been so lack luster they would have received similar complaints.
If you look at the mods made since the first chasing mods, they all have to stay on a specific area or lose the police.
Like here you can clearly see the police is right behind the player and you just lose star rating anyway.
It's the same problem pretty much even without mods where some quest you got cops driving away with a car and you can trigger the police chase.
In 1.21 I think the police really started to chase you really long periods if they remained in vision. In 1.22 they still were fixing some spawning issues.
I think 1.3 police chase would likely happen and they've been testing the functionality probably before game even launched, it's just there was always some thing they needed to add into the game and then test again and figure out new things to tweak constantly. I think it could have been as late as 2020 January where they started to work on police chase among other mechanics, where the delay on march was due to these mechanics being far from ready, along with the work to make game run in any level on old consoles.
In December they probably had worked most kinks out and made the game run "surprisingly well" on consoles, where testers were able to finish the game, but the game crashed a lot, they also had issue with police chases and they had a decision to make, whether to delay the game half a year, get everything working smoothly and getting police to work (where there still was no promise that half a year would be enough) or just release it and work out some easy kink to spawn police meanwhile the police mechanism is finetuned.
Also for modders it's easier to create these mechanics when there's 1 platform it has to work, PC, while CDPR is making the game on 7 different platforms, you have to make sure it runs on every single one. And it cannot cause crash for example like some mods do. You don't want to create more problems.
Mods are also not really advanced, they basically utilize what the game has given to them, most earliest mods were just simply enabling these polices spawning in cars, which were a feature turned off.
Also of course there's other things like pathing, making sure the police behave in reasonable fashion, and don't drive over pedestrians. IF you look at the GTA for example, in GTA 2 the police I'm quite sure didn't have to worry about driving in the Z matrix at all and if you stood in middle of the bridge the police were just driving around you, police could
drive over citizens like they didn't know exactly what road even was, police could shoot citizens and
stuff like this was very common occurrence.