I propose that most of all armored vests, such as Bulletproof and Security vests be able to be attached to coats/jackets, or vise versa, while still retaining the benefit of the armored vest. This would mean that, for example, a detective can wear his trench coat and his armor in conjunction with each other, in the same slot. The main purpose of this is for cosmetics and the ability to hide armor vests under some types of coats/jackets. From a practical perspective, it also does not make much sense to not be able to wear a armor vest and a coat over it.
Of course, armored vests wouldn't be able to be attached to armored coats/jackets as that would be stacking armor values. Armored vests would also not be able to be attached to any sort of exosuit such as hardsuits or space suits. The reason why armored vests would attached to jackets/coats and not be able to be attached to jumpsuits is because then somebody could wear another armored vest or coat over a armored vest; Thus stacking armor. For some armored vests, such as Ablative or captains carapace, would be entirely up to you peoples as I can see how that may be a balance issue.
Please let me know if there are possible issues with this idea, why you disagree/agree with it, etc.