Into becoming an elf or more concisely to adopt a Merrish POV with the Black Books? What would be the ultimate knowledge one would seek in Apocrypha? The secrets of immortality. Isn't that something that the Mer would strive for while their polar opposite 'the Nords' seek a glorious death? Maybe I'm overthinking this, but in between TW3 I've been working on Dragonborn and that got me thinking...

He did try and trick the Nord's into becoming Aldmeri, true, but that's not quite the same thing happening here I figure. There's also the issue that the PC could actually be Aldmeri anyway. The odd thing in play here is that had Miraak escaped, he would have still spread Mora's sphere no matter what happened, but he was more concerned about retaining "control" (if you could call it that) over him. Which frankly, is pretty odd for a Prince.

Mora isn't above subterfuge once his followers stop operating effectively, but I don't think his motives here go beyond trying to keep a shiny Dragonborn under the iron shod grip of his noodly appendages.