Simple question: Does My Fair Lady need to be remade for any particular reason? Even if with Keira Knightley and (possibly) Daniel Day-Lewis in the Audrey Hepburn and Rex Harrison roles, respectively? I've always thought Hepburn was fairly miscast in that film and Harrison, who made a career out of playing that role, just yelled the words out. So it's not like it's perfect. Yet despite those flaws--or maybe, in terms of what makes it still reasonably endearing (despite its defeating Dr. Strangelove for Best Picture and Harrison defeating both Peter Sellers for that film and the great Peter O'Toole for Becket), because of those flaws--it's still seen as a classic, a movie that gets a number of things just right. So, why remake it? Maybe because they can, and maybe because they think they can actually make it better.
I'm always more inclined to accept unofficial "remakes." For instance, Baz Luhrmann's Australia appears to be wanting to desperately be "EPIC" like Giant or dare we say it, Gone With the Wind and other traditional epics, this time with a strong Aussie twist.
David Poland speculates as to who could be cast in this thing...
I think I like the Kevin Kline idea by one of the commenters myself.