From reviews I'd read, the HP WITH the Gloss Enhancer was only about as low-bronzing as the latest Canons and Epsons without. The HP ink was otherwise behind Lucia EX and Ultrachrome HDR (it was more like the x000 series Canon inks and the pre-Vivid Magenta Epson inks), and the gloss enhancer brought it up to the latest standard? I have extensive experience with Canons and Epsons, but have never used an HP larger than 13", so I'm going from what I've read here...
That said, a gloss enhancer might help the latest generation of inks as well. It seems like a 14-ink printer would be justifiable, and the ideal combination might be something like (simply combining what already exists - not wondering what something entirely new like a purple or brown ink might do, or three strengths of magenta or cyan):
11 channels of Ultrachrome HDR (the Epson orange/green combination seems to be a little better than Canon's red/green)+
Blue similar to the Lucia EX Blue+
Extra Black that Canon is using in the Pro-1+
Gloss Enhancer
It took about ten years to go from the first pigment-ink printers with weird gamuts only the size of sRGB (and oddly shaped to boot) with all sorts of strange metamerism and green casts to the Ultrachrome HDR/Lucia EX generation with well-behaved gamuts that cover most of Adobe RGB and exceed it in some areas. Once we got there, we've sat for five years. There are colors the latest sensors can capture that no printer can print (I'm thinking of some of the recent Sony full-frame and MF sensors with excellent dynamic range, as seen in recent Nikons, Sony's own cameras and now he 50 MP medium format CMOS sensors), and there are colors a Canon can reach, but not an Epson, and vice versa. Would the 14-ink printer above cover everything a Canon OR an Epson can reach today? Probably... Would it cover everything the latest Sony sensors can capture? Perhaps.
Whether it reached the edges of what the most recent sensors can do or not, it would be more transparent to artistic intent than any printer we have, and that seems reason enough for someone to build one. Photo technology is ultimately about taking what we see and transferring it into a final form, and it seems like, while the printers we have are very good at that, better is possible with current technology...