If they actually do pull the trigger on a Peter/Lily romance, it will never work from a press standpoint.
As someone who's taken courses in "African Literature" and "Black Cinema" in college, I can see that some comic fans will reject the pairing as being "an attempt at being overly politically correct."
Meanwhile, there will be people who will complain to the press (assuming the media picks up on the story) that Lily is too lightskinned or that she is betraying her black heritage by dying and straightening her hair (Maya Angelou famously has decried black women who do not have some form of afro, or "natural style" as she calls it).
A Peter/Lily romance would not end well in the media. I know a lot of fans were critical of Howard Mackie portraying Randy Robertson as a "Rastafarian Yuppie," but that was probably a more positive portrayal of the modern African-American (succesful and upwardly mobile) than the ditzy, out of touch with her heritage Lily is.
The other posters pretty much summed it up. It won't work, but it has nothing to do with race...
a.) Marvel won't allow it long term after they just went to all the trouble to end the marriage. Peter will never be married again. Pretty much any relationship he's in is doomed to failure (probably b/c of Spiderman).
b.) Fans won't accept it b/c she's not MJ (or to a lesser extent Gwen, which honestly seems to be who a lot of the anti-marriage crowd is).