The DD67000 port assembly is cast aluminium

I have seen a 15 inch port on a 2225 system many years ago.

In Alex Bradminoff and Don Davis red loudspeaker book they make reference to vent area equalling cone area

A port can be constructed out of timber and baced where one enclosure wall forms one side of the port

Perhaps a point to consider is pipe organ resonance with long ports and volume occupied by large ports

A port should be ideally at least one diameter from any enclosure wall
If you consider enclosure construction then the practicality of large port area becomes a limiting factor

I think the associated concerns of power compression points to the use of multiple subs where the total power is divided across 2 or more subwoofers. For example 1000 Watts into a voice coil is on the spectrum when a large portion of that is lost in heat. Stacking of subs then becomes a reality.

Others claim tapped horns are more effective at high power levels

I once heard Steve Schells bass horn
On just a tiny digital amp it was dynamite. Deeper, faster and more dynamic than any bass reflex system
I would not mind hearing the OMA bass horn with a 21 inch driver