There's been no official announcement about who will take over from Marcus. Graham MacDuff (who plays Lancelot) is First Cover Arthur and will be playing Arthur in Wimbledon on June 3, so it's possible that they will simply move him up to take over as Arthur in August or they may still be looking for another "name" to take over.
I loved Spamalot when I saw it in the West End - but then I've always been a huge Python fan since way back in the 60s! I don't know how good the tour production will be - I'll be posting my views after seeing it on June 3.
THEATRE 2020: CURTAINS**** LET'S HEAR IT FOR THE GIRLS***** WICKED***** KEITH RAMSAY TAKING NOTES WITH EDWARD SECKERSON***** KAYLEIGH MCKNIGHT CONCERT***** RAGS***** ON MCQUILLAN'S HILL** DEAR EVAN HANSEN***** THE JURY***