I would love to be able to shoot my buildings like previously and damage them, but having turrets kill each other especially on space platforms is definitely not what i had in mind.

It would be nice if we could enable collision to player-shot bullets only or, alternatively, make turrets ignore each other when in close proximity? I'm sure there are many ways to approach this, I just wanted to bring this up in the hopes that an elegant solution can be found.

It's definitely more possible now in 2.0 with the use of collision masks but I'd need to think about it quite a bit. e.g. bullets don't hit turrets or walls but do collide with everything else? Another option is radius locking so they don't turn too far and blow each other up. But that obviously comes with other issues.

There isn't a way to cleanly do it based on proximity without some cursed - every individual bullet has a countdown that is checked 60 times a second - type thing which would be terrible for performance.

How about an option for player fired bullets to collide with everything? It wouldn't apply to turrets but does let you personally take things out.

EDIT: Actually that last option won't work because the bullet type is defined by the magazine.

bullets don't hit turrets or walls but do collide with everything else?

I think for starters that's a good pick for a filtered approach that applies to everything, yes, even if it is kinda hardcoded and inflexile when it comes to accounting for other mods. Basically your aim should be to prevent regular wall designs from self-destructing; so that would mean no walls, gates, flamers + piping, lasers + power poles, turrets + inserters and maybe lights.

Radius locking sounds like a more versatile solution but i feel it may come with a ups penalty, depending on how you can achieve this.

Finally, changing it for the player sounded like it would achieve a big part of the desired effect. Maybe you can do something with factions to filter who gets damaged? Alternatively, can you forward to a damaged entity the instigator of said damage? If you can, maybe you can just check if source != player then restore the damage back or not deal it in the first place, whichever is more accessible - thus achieving the "player damage only" effect.

I am also curious if the new "target priorities" mechanic can be useful in any way, not sure if it can be used to create a sort of whitelist when it comes to who actually receives the damage or not.