Well, putting a new optional rule is well down the list of things to code.
I also find it a very strange rule. Consider D-day: Six divisions invading, plus three airborne divisions, plus some specialized units. Three corps, plus some divisions. In WiF, one might get six corps, representing follow up forces.
Ships represented by WiF counters that provided NGS on D-Day:
Utah beach: Nevada, Quincy, Tuscaloosa, HMS Enterprise, Hawkins, Erebus, Black Prince
Omaha beach: Texas, Arkansas, Glasgow, Bellona, Montcalm
Gold Beach: Ajax, Argonaut, Emerald, Orion
Juno Beach: Belfast, Diadem
Sword Beach: Warspite, Ramilles, Arethusa, Frobisher, Mauritius, Roberts
(I may have missed some. If so, my apologies to any ships and crews I omitted.)
Even assuming that some of these ships provided defensive shore bombardment (and yes, the Allies were using that optional rule ), limiting the amount of shore bombardment to three, or even six, ships is ridiculous.
I thought I knew how to play this game....