The solution I've found (years ago) is to use the model callback PostLoadFcn and to fit the view programmatically every time the model is open with this script :
top = gcb;
while(get_param(top, 'Parent')~=0) %or split
top = get_param(top, 'Parent');
end
all_Subsystem = find_system(top, 'FollowLinks', 'on','BlockType','SubSystem');
for i=1:numel(all_Subsystem)
set_param(all_Subsystem{i},'Zoomfactor','fit to view')
end
