Good morning, Dryden. In reverse order of your points.
The object can be found if you visit wikipedia for the 4,2,7 you've exposed in the grid. The initial site tells you about the history (from as far back as Heraclitus, so the paradox is akin to the river and the changing water in it. But then there is reference to another wiki site with a list of different examples. The setter's chosen object is referred to there. Also, as commented previously on this thread, the setter makes a big hint of the object with the sentence "This in turn..." If still stuck you might want to google random words from that sentence together with the 4,2,7.
I thought the concept of the puzzle was good, the construction was generally okay, but the process of making word changes became a bit of a bore. I'm not convinced by my own suggestion that there is a loophole for across clues not to become intermediate non-words, but if true, that ambiguity is a very big negative for the puzzle. At the moment I don't see any other options.
15D, if I have it right, is a bit lame in that the change is simply from a noun to the associated verb's past participle. And the 2011 TCD doesn't include a version with an 'e' in penultimate place. But maybe I have that wrong too...