Little Ali would be just about to turn 26 at the time of the anniversary, not sure how old mehmet's children would be but Haluk Belinger and Ishia Bennison are still acting so would be good to see them again too, maybe as owners of the old Argee Bahgee and turn it into a Turkish restaurant (I always prefered Mehmet and Guizin to Ali and Sue)
Other original/older characters I'd like to see return, for guest or extended periods, would be Annie Smith (Mary's daughter, as Linda Davidson is no longer acting. Not sure why she'd come back though.), Carmel Roberts (she could still be a Health Visitor and her daughter Aisha (played by her real daughter, Aisha) could return as well), Dr. Legg (could return to see Dot), Lofty (Dr Legg could drag him along maybe), Martin and Wilmott-Brown (could maybe unknowingly get involved with Sharon and The Albert).