I thought that they would simply release a web update for the FRCS and other FR books which convert any needed data to 3.5. If the books are already printed, I'm sure they've had the complete rules worked out for some time now, thus I'm sure they have plenty of time to convert some FR things over to 3.5, especially things in Magic of Faerun, which has a lot of magic items and spells that might need conversion.
While the new FR Player's Handbook MIGHT contain this information, I doubt that will be the only or even the primary point of that book.