Don't forget Oly does have a good history of making housings for larger cameras. Best bet is the housing for the EM5 will be a cross between the old E-System Olympus PT-E05 Housing - Olympus E-System Camera & Housing Systems - Optical Ocean Sales Underwater Photo - 800-359-1295! housings and the newer E-P series. Hopefully closer in size to the newer housings.
But as mentioned it may be a while, there are rumors that Nauticam may make a housing for it.
But as mentioned it may be a while, there are rumors that Nauticam may make a housing for it.