This is more for curiosity and experimentation than anything else.

What's the possibility of mocking up a variable intake length system to a Honda (D or B series)?

Like, fabricate a CAI like intake. Also get a short ram intake. Combine the two with a 2 to 1 Y tubing which is connected to the throttle body. Between the short ram and the Y, is some kind of a blocker like a butterfly throttle or something (like the exhaust cutout controller) controlled by some mechanism that opens the ram when RPM's are high (like use the VTEC as an activation signal).

The CAI gets the resonance benefits for midrange, and the ram opens up at the high end.