Neither bmi or Virgin Atlantic have set ATL has a priority. Airlines apply for the most random route authorities all the time for the hell of it. Atlanta does not suit Virgin's destination profile at all. They aim for major leisure markets, and Atlanta is not a leisure market. And bmi has already set thier priorities...Chicago, Denver, Miami, Seattle, and Washington Dulles.
Varig and JAL are not returning to ATL. And it's for one simple reason: Delta. Varig pulled out not long after DL started ATL-GRU and JAL pulled out just after DL started ATL-NRT. They simply could not compete.
Atlanta is working very hard to attract African carriers (though SAA's succsses is due to the Delta deal, and little else), and the market for African carriers will grow in the next ten years. They are competing with Miami to get a head start on becoming the US-Africa gateway. I know Ghana Airways has shown interest in ATL, but that was about three years ago. El Al has also shown interest. I believe it was in 2000 that they announced the start of TLV-ATL-MIA-TLV flights, but they never started.