Look, seriously, if you want to print on transparencies or socks or doors or linen or cheesecake or aluminum siding or your hamster, white ink is necessary because those items don't naturally come in "white." But if you're feeding paper or indeed almost anything opaque less than 20 mils thick through a photo inkjet printer, chances are excellent that it is already white, and such a white that there's no reason in the world to try and improve on it. And if there's parts of it you don't want to be white -- you print on them so they are some other colour!
White ink isn't needed for fine art printing on paper or canvas.
I'd take a high gloss coating before I took white, any day -- oh, wait, my HP has that.
Now I'll eat my words and say that if I want to print bright white highlights on real hand-made paper, I'm SOL. But -- and read carefully -- that isn't what these printers are for. They're designed to print on white or near-white media. They're subtractive colour mixers. You're looking for a full spectrum printer; that's down the hall.
Don't be complaining because your horse doesn't climb mountains. But neither does a goat carry you and a hundred pounds of gear all day across the pampas. Hammers don't drive screws well, either. Wrenches can open beer bottles but you don't want to drink from them once you've done so. Understanding the intentions and purposes of the equipment is how you learn to master it; not by ragging on what it doesn't do. There's stuff out there that does do what you want; it weighs five tonnes, is bigger than a shed and costs more than a Porsche. Maybe Epson or HP or Canon are planning a white ink. But I really really doubt it will be available anytime soon, for all the reasons explained to you already.
Keep dreaming, please. But realize the practical limitations of what there is, and use those to your advantage. Or, find another route to the solution entirely. There's money to be made, no doubt about it. Find out how!