Also, we retired those ladies too early. They are well suited for the new point defense lasers, railguns, and hypersonic conventional 5-inch shells we have now. Plus, those 16-inch guns could probably fit a mean gun-launched missile.
Dear Gods, NO! We reactivated those ships in the 1980s for a single specific purpose, that is to launch nuclear Tomahawk strikes against Soviet installations around the North Cape as part of the Maritime Strategy. Their size made them seaworthy enough to operate in the grim weather conditions up there and they could hold the speed necessary to keep up with the carriers. The cost of bringing them back (and it was a real minimum-level level conversion) was roughly the same as that of a Perry-class frigate. Once that role went away with the end of the Cold War, the ships were expensive white elephants. They are very costly to run and they each have a crew requirement equivalent to six Arleigh Burke class destroyers. In a Navy where economizing on personnel is a primary requirement, spending that much money on four ships with no viable role in the fleet is not justifiable.
I know Trump contemplated reactivating them
No, he didn't. He did, at one point, ask why they hadn't been reactivated, got the explanation why and never brought up the subject again. PDJT asks a lot of questions as part of his learning process (he, thank the Gods knows what he doesn't know). That doesn't mean there was any serious intent to do so.
and they seem well suited to act as defensive AA/counter-IRBM platforms for the carrier groups if you swapped out a couple of the 16-inchers for bunch of VLS cells.
No they are not; they are totally useless in that role. They don't have the radars, they don't have the command spaces, they don't have the weapons, they don't have the battle management capability and they don't have the power generation capacity. To convert them to an AAW ship or to an ABM ship would involve dismantling them down to the waterline, gutting what is left and reconstructing a new ship on the resulting hulk. The end result would be greatly inferior to a purpose-designed Burke and be far more expensive. She would also be a major liability to any fleet operations and would blow the defense budget out of the water.
As to stripping out main battery turrets and replacing them with VLS nests, have you any idea what is involved in doing that? The turrets and their barbettes are an integral part of the ship's structure. Take them out and the integrity of the hull is compromised. It can be done, sort-of, but it is time-consuming and costly. The usual way of playing games with a main battery is to simply pull the turret from the barbette, build a light structure over the top and emplace low-impact weaponry (40mm guns, other light weapons etc) on top using the structure and magazines etc already there to serve those weapons. At a guess, the most we could do would be to stick either some Tomahawk ABLs (if any are left, they've all been pulled from service and I don't offhand know if any have been kept in storage) or Harpoon quad launchers.
Messing around with main battery turrets like that also causes massive trim problems. Overall, this conversion would be so extensive there would be nothing left of the original ship. This is why similar conversions in the 1950s were abandoned. Much quicker and less expensive to build an additional DDG-51 and we get a more capable ship at the end.
Though you'd probably need to strip a bunch of parts from the other museum battleships in order to get them fully operational again.
No, we can't. That's already been done and everything that is worth taking has been taken. Any spares we need have to be custom-made.
Bringing back the battleships, even in their present form, is economically, technically and operationally neither possible nor desirable. They are doing their most useful duty right now, inspiring visitors with the glory of sea-power and (just possibly) putting the idea of a career at sea into the minds of some younger visitors.
Shipboard tech has advanced to the point we could retrofit them with modular Engineering systems and electronic tech. We can do things now that we could not do 10 years ago in Marine Engineering. So bringing them back into service is not as costly as it would have been a decade ago.
Sorry, that's not correct either. Say again, to bring back the Iowas with any kind of useful role would involve stripping them down to the waterline. We'd certainly have to remove the armor deck in order to get below and start changing the machinery. We would also destroy the ship's stability in the process. She'd need an entirely new upper hull and superstructure.
To put this simply, there are no conversions possible on the Iowas that would provide a useful ship at any kind of reasonable cost, time and labor expenditure. Anything that a proposed conversion would achieve can be done much better by an Arliegh Burke at a fifth of the cost (and a sixth of the crew requirement.
Sorry, I know its a lovely romantic idea to bring battleships back again but doing so is just not practical