I still don't see exactly how this is necessary, beyond Johns wanting to cram some more dramatic elements into the Green Lantern mythos by somehow trying to make Natu divided between Sinestro and her duties to the Corps, which is all this really is.
It was enough for me that Natu was an interesting Korugan character who obviously had to balance her duties as a Lantern with the fact that she could become more and more like the man every single one of her people hated, and this just spoils it, to me, despite adding a vaguely interesting legacy idea to Sinestro and his ring.
If Blackest Night turns out the way I personally think it will - Johns talks of the aftermath as having 'one hero's redemption ending, and another's beginning' - That Sinestro could rejoin the Green Lantern Corps in some degree, and make an unusual father/daughter team, fraught with annoyances because Natu's currently with Kyle. Either that, or Natu outright revokes him, or it takes the really obvious current-DC idea that having evil parents means that you too are evil, and Natu will be donning a yellow ring or whatever.