[joeysteele]

It's a good idea, it will be a success so little doubt it will be renewed,2 years will be a good showcase for it and then a further contract can be done later.

Often the problem with 5 year+ deals the producers etc take all for granted knowing that deal is done, this will keep everyone on their toes to make it a success.
In the words of Channel 5 they are delighted to have won BB for the Channel so they will certainly want to renew it when it improves their income and ratings, in fact, they would be totally crazy not to renew it in that scenario.