There are some great aspects to the Seattle Seahawks being sold. One is that the proceeds of the sale (likely to be between $7-10 billion) will be donated to charities. That is good for humanity. What might not be good for NBA fans, though, is that the football team being sold might affect the SuperSonics' return.
The reason is the size of the market and the potential buyers. While multiple professional sports franchises have been up for sale at the same time in the same city before, mostly in New York City or Los Angeles, which are obviously big enough to host multiple franchises in all of the big four sports leagues in North America.