Jake, thank you for posting this important topic.
Just yesterday, I spoke with a former President of the HCCA about this. When he was President, he proposed just what you described to save the HCCA from dwindling membership and expenses by consolidating under the AACA umbrella.
My issue with the current HCCA is that although the club allows 1942 & older vehicles, about 40% of their members do not own pre-1916 vehicles, and members with these vehicles are not supported by the national club.
They have no vote in national elections and cannot participate in national tours.
The current HCCA board refuses to even list these members in their roster.
Although the HCCA has several "Registries" for specific marks & vehicle types that include 1942 & older vehicles, none are fully supported by the national club.
I 100% agree with your statement with respect to the HCCA leadership: "club's leaders feel very prideful that giving up a national footprint to become a "chapter" of the AACA would be sacrilegious."
Consolidation under the HCCA would be more cost effective by eliminating the high cost of individual club magazines, annual dues to only one club, and shared resources for libraries and museums.
Consolidation would offer the best of both worlds with more opportunities to meet everyone's needs with more car shows, tours and other events that everyone can enjoy.