Jake was something of a fluke. Magic chosen people work under different rules than the rest of us. As for more like him, well that would be up to Eywa, wouldn't it?
Rather than engage in a one sided gene flow, the good people of Pandora should help humans learn to See their own planet again. Gaia might not be dead quite yet--Earth has come back from Mass Extinction Events before.
PS there's a fanfic (a good one actually) where the Earth is finally utterly destroyed (on purpose) and a single ship of survivors comes to Pandora.
Terra's Tears Chapter 1: End Of The Beginning, an Avatar fanfic - FanFiction.Net