That would be yet another name-blog column! :) The exact origins of creative trends (as opposed to the forces that drive new trends to popularity) can be very difficult to track down. The backwards-spelling trend seems to have come to recent attention primarily for Nevaeh. In the case of Nevaeh the distribution and motivation for popularity seems to come most strongly for evangelical Christians (of all ethnicities) and parallels a slightly earlier and less dramatic fashion for Heaven as a name. (If I were looking at it as a long-ago historic practice, I'd be tempted to interpret the backwards version as a taboo-avoidance approach, but I'm less confident about that in a modern context.) But if you look at the online buzz about backwards spelling as a way of deriving new names, it currently seems to be driven by baby-name sites and bloggers as a "creative idea" rather than emerging from random independent decisions. So this may be a case where the original idea had a very specific motivation but then the manipulative process was added to a general toolkit.

Keep in mind that modern society does not have a monopoly on startling creative fashions in given names. 12th century England saw a brief explosion of "fancy" Latinate names for girls. The rise of surnames-as-given-names in England seems to have begun as a purely mercenary practice: naming a child after the surname of a godparent or relative in hopes of attracting large gifts and inheritances. The Reformation was the main driver for the adoption of random and obscure Old Testament names. And let us not forget the rare but memorable Puritan phrasal names.