Oh, I don't think that long range artillery is a viable path to take.
But it might appear that way.
When I say long range what I actually mean is 'massive'. I mean possibly some bright spark hits on rocket boosted shells, a concept that should work for BB sized calibers, but I see more of an 'really big is better' approach.
So you end up with a ship mounting a monster gun, facing backwards.
The turret is extra fancy to allow both good elevation and speed up reloading, so thats a mechanical nightmare.
Armor is more an product of "The ship will shake itself apart if we fire the main gun" than "We might get shot at".
On the plus side all ranging shots are done with HE with a special fuze for underwater detonation, which for most targets turn out to be more worrisome than AP, owing to the fact that the HE charge rivals several depth bombs at once going off very close.
It's in theory a design that can outrun anything short of the nimblest DD and the odd cruiser but even those, so the vision, ought to close slowly that the maingun can take care of them.
In practice it's a design that can't run down anything (It needs to turn away to unmask the maingun), fires a shell that gets picked up by the AA radar (allowing evasive actions), still doesn't outrange carrier aircraft and needs enough steel and explosives that (assuming it has to refill it's magazine once) that the Ratte suddenly appears quite reasonable.
It's main result is a general up-gunning of all Navies that can and a lack of siege arty in Germany - relevant factories are mostly busy producing the monster gun and making it into a railway gun is... interesting.