I've got a compromise.
Renumbering the current 9th, 10th and 11th Doctors would only cause confusion to viewers who have not watched Day of The Doctor. It would also be a serious spoiler leak of the 50th anniversary special if we started calling Matt Smith the 12th Doctor. So lets keep Eccelston as 9th, Tennant as 10th and Smith as 11th.
Capaldi however is the 13th Doctor because his regeneration happens after the events of Day of The Doctor.