TL;DR
I wish individual entities, like turrets, were more customizable via an equipment grid.What ?
More entities ought to implement equipment grids, specifically turrets. Rather than unlocking higher tiers of turrets, you should unlock higher tiers of equipment modules _for_ turrets. So instead of ExtendedRangeMark3RocketTurrets, you have plain old AmmoTurrets which you add to it's equipment grid 3 ExtendedRange modules and a Rocket Ammo module. This mod https://mods.factorio.com/mod/equipment-gantry shows it's possible to automate this process. This does not preclude the possibility of "mark2, mark3" entities, it simply allows another path forward.Why ?
1) decluttering your recipe bookWhen adding new entities, either through modding or through research, you end up with a lot of very similar recipes. For instance, through mods you can add a million varieties of of turrets, each with their own range, efficiency, ammo, etc. (for instance https://mods.factorio.com/mod/scattergun_turret) It makes you recipe book very "busy".
2) flexibility and more opportunities for tech tree progression
Each of these turret equipment modules can be researched to higher tiers, so now you have many more technologies to research. You can put all your research into the areas that interest you. So if you want "sniper" turrets with long range and slow speed, all you need to do is research those techs and unlock those turret modules.
3) Increased complexity
Now you not only have to make the turret and the ammo, you need to make and install modules into individual turrets.
