Kiefer Sutherland would be my favourite guest announcement - he's at Wickham Festival with his band on 4th August so possibly could be in UK the week before for LFCC?
Failing Kiefer ... Kevin Bacon / Emma Watson / Scarlett Johansson
Not sure if this ones been guessed yet but how about David Jason? he's older so not likely to do another con, he's been a lead, don't think he's done a convention before, he's a UK legend
Wish List
Any of the Goonies
Millie Bobby Brown
Jeffrey Demunn
Steven Yeung
Kiefer Sutherland
Daisy Ridley
Kevin Bacon
Emma Watson
Elisha Cuthbert
Jennifer Morrison
Bruce Campbell
Any of the main cast from Game of Thrones