Don't think we can realistically fit CIWB on any Escort hulls other than the Ketch (even the Schooner would be troublesome).
The inclusion of Holo-Fields (which is a non-brainer) only costs 1 System slot but Holo-Fields+Grav-Shield is such an infuriatingly good combo against non-AoE attacks (AoEs are rare in space combat) that ideally we will want them on pretty much any ship that can reasonably fit them.
Grav-Shields however cost 2 slots leading to a total of 3 once the Holo-Fields are factored and that is quite a bit for the smaller ships as outside of the Ketch Hull (7 System slots) 3 slots represents either half or the majority of a ship's system slots.
For reference this was the winning design from the Frigate vote:
[] Void-Sail Ketch
-[] 1x Heavy Starlance -1 Heayv slot
-[] 1x Fatetwister Cannon Weapons Battery - 1 Weapon slot
-[] 2x Æthersail - 2 System slot
-[] 1x Plasma Thrusters - 2 System slots
-[] 1x Las-Lance Point Defense Battery -1 System slots
-[] 1x Holo-Field -1 System slot
-[] Trade in one weapon slot for 1 System Slot
-[] Grav-Shield - 2 system slots
Based on this the obvious approach if we want to fit a CIWB would be to drop the PD and one Aethersail to free up the two System slots needed for the CIWB, while the reduction in speed kinda sucks most of the other Frigate designs that we've seen from other Factions only had 1 Aethersail and 1 Plasma Drive so having the same engine loadout probably isn't that bad.
Unfortunately almost all our existing ships tend to use hulls which prioritize Weapon slots over System slots (only the Ketch doesn't) so it makes coughing up the extra System slots for CIWB a bit troublesome as we'd essentially be inverting the ship's inherent Weapon slot bonus just to reach System slot parity with the hull forms that favor more System slots.
Regardless, I wouldn't go all in on CIWB over PD as while CIWB does hold an advantage in NEP cost and the ability to hurt starships a CIWB at least on the escort scale only has 1/6 of the weapons of a PD battery and I doubt it gets any better the bigger a ship you get.
Each PD battery is 60 individual weapons (for an Escort anyway) whilst CIWBs are 10 individual weapons (again, for escorts). This might soundlike a lot, but keep in mind even a piddling little destroyer is pushing a full kilometer or more in length---ships in 40k are VERRA LORGE.
That reduction in volume of fire and the increased size of the weapons hampering tracking are why Mechanis stated that CIWB's are worse at dealing with strikecraft and ordinance compared to PD (kinda vague as to whether CIWB actually has a relevant range advantage).
Essentially, the difference is that Point Defense batteries are (comparitively) small, fast-firing weapons that are very good at tracking fast moving targets (fighters, ordinance, boarding craft,) but lack the power to do more than maybe some surface damage, in the same way a machine gun or Bofors mount would be effective for engaging most world war era aircraft but won't do much of anything to a battleship's main belt, whilst Close In Weapons are more like dual purpose guns---trading some of their effectiveness against fast movers to also be a threat to other ships, even if, lacking the power of full ship scale Macro-Weapons, they are only effective at short range.
And yes, screening with point defense and or CIW batteries is definitely a thing. Effectiveness may vary--- if you're going for "#AmericanAAscheme" you're talking about probably at least one CIW battery and two or three PD batteries, but given most ships are mounting either one or none of either (and often the latter) even one is better than a lot of ships get.
I'd say with Escorts we could either design a 2nd Frigate scale escort with CIWB or just field enough Nettles which do have PD to complement a CIWB refitted War Ketch.
For our Capitals we could either figure out if going #AmericanAAscheme is feasible or go with a similar approach as the escorts where we have say the Carracks rocking PD while the Brigs have CIWB.
Edit:
As is the Holo-Field+Grav-Shield combo makes any ship equipped with it infuriatingly difficult to damage with Weapons batteries and the only real counter other than overwhelming numbers is either strikecraft which can keep making attack runs until they hit us or AoE weapons like Nova Cannons.
Nova Cannons are limited to the Imperials and any Orks which have managed to loot them (so less common than Imperials) but strikecraft are universally available to all factions.
With how common strikecraft are we will generally get more mileage out of PD as strikecraft are the only thing that will be able to consistently catch our ships other than Necrons and other Eldar.