They'll accept it the picosecond they think that they'll make more money if they do than they will if they don't. They'll be supporters of Bitcoin instantly if they conclude there's more profit to be had by supporting it than attempting to interfere with it. Whether they'll ever actually conclude that is the variable, but they're a corporation, they'll always do what they think will put the most money in their executives' pockets.
It's never easy to predict what paypal will do. But i guess for bitcoin to have a chance to get accepted by paypal, and idea would be to do what Linden Lab does, stop calling the currency a currency, and just call it a
"token" or
"a license right to exchange services and goods against".