I agree, that at least equipment like AAA, radar etc. should be upgradable.
Yes I hope this will upgradable as it historically many ships got AA and radar upgrades.
Also I don't know how it's implemented in the game but ASW weapons should also be upgradable.
From a gameplay perspective if AA can't be upgraded carriers and naval bombers will be much more overpowered than historically since most of the starting fleets would have very bad AA capabilities. Likewise if ASW can't be upgraded all your starting destroyers will basically be useless against new subs.