I was mildly interested in this toy when it first appeared, and even though I'm not too keen on the design or its source material, I wonder if scratchbuilding a "kit"/toy of it wouldn't be possible.
I had a lot of text written breaking down the way it seemed like the design was laid out, but I think the biggest flaw in the ET rendition is just that the proportions are out of whack. Not altogether anything new to Macross, though. The Yamato and Bandai VF-1s all look not quite right in any of their three modes. The most well-proportioned VF-1s, the Hasegawas, are built as three separate non-transforming kits to avoid this issue altogether.
There's enough consistency across modes in this design that I think it could reasonably be engineered to transform without sacrificing in the looks, but that would make for a very delicate toy. ET have, I think, simply traded more of the "model" aspect in favor of the "toy" aspect.
EDIT:
That's my assumption right now as well. Behind the upper air intakes there's actually just empty space until the arms/head, with that space broken up by the leg swing bar (more of a flat expanse than a bar) and other internals. The lower vertical fin is, I think, meant to break up that empty space, but it doesn't do a great job.
The ET toy doesn't try to emulate the legs' swing bar mechanism, which is, as said, a sort of hinged rectangular piece. Instead they went with their swinging slanted bars setup. It trades on "lineart accuracy" for sturdier joints.