I personally see absolutely no reason why someone with the skills shouldn't be able to try and duplicate damn near anything they want to, for their own use and enjoyment. Hell, there are tons of schematics on the net, and plenty of pictures of the insides of components where a competant DIY'er can make decent guesses as to how they should be laid out and constructed. Whetyher it is a speaker, amp, DAC, turntable, cable, whatever. Of course it won't be the real thing ... but that's not the point. It's the thrill of testing your own technical prowess and reaping the benefits and enjoyment from your efforts.
Remember, this is the highest form of flattery.
Of course making it with the intent to sell it for profit, or making a business out of it is a no-no. But eventually this guy will get the bug to replicate something else, so these will likely be sold to someone. Hopefully it will be a private sale and not posted on Audiogon.