Completing all of the challenges for this week (week 3) unlocks another loading screen:
Along with the above, the BlockBuster challenge loading screen for week 4 has been leaked:
Here are the locations of hidden Battle Stars for week 3 and week 4 challenges thanks to Reddit user GamingSoldiers
The bottom Battle Star is for Week 3, with the top left Battle Star for Week 4.
Credit to TwoEpicBuddies for leaking the loading screen for Week 4